It is not necessary. To be an author you should have participated to the work. iny opinion, to find the financial funding is not enough, you should be part of the research.

In my view, it depends on what the topic is, and if the selected case study similar to others in different countries

It is not necessary to add one or more foreign authors in manuscript. Publication of manuscript totally depends on the quality of work and its contribution towards new knowledge.

To be honest, I'm a bit shocked by this question. Is this really a thing? One should never have to invite authors just for the country they work/live in or the institute they work for. Of course international collaboration is great and can be helpful, but that should then be a true collaboration throughout a project and based on expertise and contributions - not just authorship to increase publication chances. 

I think that you can get more update information regarding  the scientific English rather than normal  english.

The question is do the authors include
foreigners? Authorship is not based on geographic location. It is based on contribution to the paper. Contribution to conceptualization, method, data curation, analysis, write up and review. Without substantial contribution to any or most or all of these, no one qualifies as an author on a paper

Short answer is No.  International Committee of Medical Journal Editors (ICMJE) criteria specify that all material contributors to a manuscript should be recognized with authorship, but also that all authors must have made material contributions to the manuscript.  Adherence to those guidelines, in addition to the innovation, significance, and scientific merit of the work (clarity/reproducibility of methods, quality of data, relevant controls, appropriate statistical comparisons, etc.) are more important than origin country of the authors.  So, I don't believe it's necessary to have foreign authors as long as the manuscript is well-written and comprehensively describes a high-quality study, including a thoughtful discussion section. 

Journal reviewers and editors should not base their desition on the nationalities of the authors of the manuscript. It should not matter if there are foreign authors or not. Having said that, there is research that shows a bias of journals to publish manuscripts that include authors from central countries rather than those that only include authors from developing countries. There is also proven bias that authors from central countries cite other authors from other central countries more than authors from developing countries, even if there is abundant research done in that area somewhere abroad. And like it's been mentioned by other responses, if an author is from an english-speaking country, publishing revisions are less focused on the writing aspect of the manuscript. 

Unfortunately, recently we see that there is a competition between researchers to increase their H-index unscientifically that has recently become common. For example: unethical and unscientific switch or exchange of the authors position between different articles.

So that, a person can simultaneously publish more than 50 scientific articles in different research areas of the relevant field in one year. How can it be possible?
It is clear that there is a deal between researchers of different papers to switch the authors positions of accepted articles. It is certain that, for example, this researcher did not contribute in a real and serious way in all 50 articles published in high-impact and famous journals. In this deal, researchers of article A, add names of their friends in the accepted article and in return (later) their friends add names of authors of article A in their accepted article B (without a real scientific contribution between the authors of article A and article B). 

Publishers or editors of journals cannot prove this or they cannot judge according to the number of authors. But databases such as Web of Science or Scopus, and especially universities and scientific centers, should consider the main score of each article to the corresponding author, or the person who has contributed the most of work according to the description of Authors’ Contribution in the article. 

 В числе авторов должны быть только люди, принимавшие участие в
 экспериментах. 

Check Nagoya and ABS regarding requirements to include co-authors from countries in which the research was performed!

Mostly important research findings are lost due to poor presentation and organization. Including co-author from abroad helps in improving quality of the manuscript and also prmotes an effective collaboration among scientific community in future

Most of the Journals usually accept papers based on scientific facts such as hypotheses and novel findings, and rejections are a natural part of this journey. Adding foreign authors may not significantly impact acceptance. But, collaborating with experts abroad does bring diverse viewpoints and encourages future collaborations. 

As an Editor of a high-impact peer-review journal, I may recognize participation of authors of multiple institutes instead of a foreign collaboration. In many cases, foreign collaborations could be guarantee to pass the first-phase (abstract overview by an Associate Editor of a journal) of the review process but may not a possible publication without reviewing the desired scientific contents in the manuscript. My experience is, accurate drafting of the manuscript, especially the use of simplified technical language, is a key to pass the first hurdle (a rejection by the Associate Editor without sending the manuscript for peer-review).

It is absolutely unethical to include an author who has no contribution from the real architecture of the said manuscript, however, we see people do it both in developing and developed countries.  

While the practice of evaluating paper acceptance or rejection based on the inclusion of foreign co-authors is widespread, it's important to discourage this approach. Often, original authors feel compelled to include foreign co-authors to potentially waive off APCs or to lend an appearance of more rigorous manuscript supervision. However, it's crucial to prioritize the merit and quality of the research itself rather than external factors like co-authorship.

Not, necessary. The paper should be technically sound, novelty should be mentioned, and the aim should be clearly should be mentioned in the abstract. the methodology and stability and validation of the paper make a sound to be published in a Scopus journal. the paper should be submitted to related journals.

Just for the sake of publication or  for contribution with respect to APC, it is not ethical to have a author/co-author for abroad. It should be based on the contribution or collaboration

Foreign author contribution matters, whereas, addition of foreign author does not guarantee any chances of publication. 

It is not necessary, you can add or not depend on the role of authors and cooperation

It is not necessary to add any foreign collaboration but it become  a need for researcher  of developing countries who can't pay high charges of good category journals. Then they prefer to include a funder as . coauthor 

No, it is not a necessity. What will be their contribution? So journal have a section of AUTHOR CONTRIBUTION, so before adding an author, you should provide details on his contribution to the work. 

It is not necessary to add an author from abroad to a manuscript. If the research work is in collaboration then we can add the name of collaborator.

Owing the possible academic collaboration and topic of interest consideration, foreign researcher expertise may be helpful and needed to improve the research work quality from study design to manuscript writing. Multicentric studies may also require the need for collaboration in foreign setting.

Dear it depends on your research. Not necessary to add co-author from abroad. However, if you have international collaborators and they contribute in one way or other, then it will be very helpful. For instant, if they provide research fund for your research project or if any one of them is native English speaker, they will improve your manuscript quality. Off course, if someone have research projects and is a well-known researcher of the field as well, he will help you in analysis, conclusion, interpreting results.it also help you in publication process, will pay the submission fee, APC of the accepted manuscript.

Yes, if a foreign Author has the same field of research and supports the manuscript through some work conducted in their research Lab otherwise it is not suitable  

 In medical science professionals from Low and Middle-income countries can offer findings that contribute to the knowledge of world science. An important issue is for example human epidemiology in childhood cancer, in which the scientists from High-income countries do not have a clear knowledge. Therefore collaborative studies should be done in all these instances. Currently, it is imperative that international collaboration should be a must, consequently, foreign authors should have an important role in this work.

I agree with all the answers given above. Despite the fact that the same manuscript was accepted by the journal, yours was refused. I believe that sometimes it also depends on the editor's choice. But naturally, they gave a few solid reasons for rejection.

No. Only researchers directly involved should be on a publication. Extra names are unethical.

There may not be direct relationship between publishing a manuscript and the authors, we may sometimes infer that some manuscripts are rejected because of unexplained reasons, even if we know that they have met adequate merits for their publication. 

No, no need. On the contrary, foreign authors are often included although they were not involved in the study.

Best

I have over 75 SCI papers to my credit in various journals. To my knowledge, no journal has this requirement and it should not be the basis for assessing whether the manuscript meets the journal's publication standards or not. 

No

To add an author should be justified by the significant contribution of the work(s), otherwise, usually acknowledge the non-significant facility provider in the project.

No, it is not necessary to add foreign-based authors to a manuscript if their contribution is not required to achieve the objectives proposed and work done. The authorship of a manuscript should reflect the actual contributions of each author, regardless of their location. Adding authors for the sole purpose of their location or affiliation can be considered inappropriate and a violation of academic integrity. However, it is also important to note that collaboration with foreign-based authors can bring new perspectives and expertise to a study, which can enhance the quality and impact of the research. Therefore, if there is a need for such collaboration, it is acceptable to add foreign-based authors to a manuscript.

Adding author name after finalizing the work is a ethical issues that shoud be avoide.

The only way that the presence of a foreign author is warranted is if the foreign author has done considerable editing of the manuscript.  For some non-English speakers, (if the journal is published in English) there are problems with authoring journal articles that use publication-grade English.  As an editor of a journal, I have asked authors to add a native English speaker to their team to sharpen the language. I have also acted in that capacity on some articles.  So, if you need that service add an English speaker to aide the text, then add an author, if you don't, then don't add a foreign author, as that practice is a bit unethical.  

It is not necessary to have a coauthor from abroad to publish; however, it is always great to establish collaboration with researchers from other countries/continents.

I think the presence of foreign author is not the necessity for publication. instead, the merits of publication should based on the methodology, findings of research, appropriateness of results and collaboration of research in accordance with current situations.

Prestigious journals do evaluate a submission just based on its scientific mertis, i.e., the importance of research question/hypothesis, and the appropriateness of the methodology used. Other somewhat important issues include the quality of presentation of results and discussion of the findings. The authors are not that important.

Rejection is not the result of absentment of foreign author (s), but rather the lacking of exposing the novelty of your work, weak or poor interpretation of your results, and improper presentation of your data. However, nowadays multidisciplinary and collaborative research are highly appreciated and easy to publish.  

While international collaboration is highly desirable and extends your research coverage, it is wrong to include anyone in your manuscript without substantial contribution to the work.

Only the people who actually contribute shall be included as authors, adding more authors just because they are foreign based is just a ghost-writing pathology.