Does getting a PhD in a language 'L' from a non-'L' country have any drawback in case of academia?

What kind of problems may he face if he moves to an Anglophonic country to be in the academia?

No matter where he did his Ph.D., he is likely to face an extremely tight job market, with many more extremely qualified job candidates than open tenure-track positions.

In general, to get hired, it is to his advantage to make himself and his work known to whatever sort of department he hopes will hire him. So, for example, it is a good idea to attend (and speak at) conferences in countries where he intends to apply for jobs.

It is also a good idea to take steps to "understand" the sorts of universities where one intends to apply. For example, from what I can tell, the "small liberal arts college" model seems to be uncommon outside the United States and Canada. If he were to apply to such jobs, it would be to his advantage to learn in advance about how they operate, and to learn something about what they value.

The question relies on the common misconception that the institution where one does their PhD matters a lot for their future career.

What will matter at the end of any PhD is the work which has been done: quality of the publications and of the dissertation itself, ideally projects and/or contacts made with the international community in the field, involvement in the academic life in general (although this is usually after the PhD), etc.

As long as one contributes to their field and establishes contacts with their scientific community, their work will be recognized everywhere. On the contrary, an isolated PhD without international publications/contacts is a hard sell even from a prestigious university.

A Ph.D. in a field is a recognition of having done publication-worthy research in that field, and in being prepared to start an independent career in that field. When that field is "Language L", it refers to research in some facet of its language, application, pedagogy, or literature (though your mention of 'linguistics' seems to imply that is not the case here). It is not intended as an advanced credential in applied language ability in that language (though one would assume some moderate language ability would be part of the skillset needed to have completed the Ph.D.).

All of that means that there is no inherent reason for such a Ph.D. to be devalued for an academic job in the field, anywhere.

That being said, while publication pedigree is the most important, pedigree of the degree granting institution, the specific department, and the supervisor do matter in the initial post-Ph.D. job. For English, I don't know, but I suspect more respected departments and advisors tend to be in the Anglophone word. I'm sure that's not universally true, and definitely not true for all world languages, but it is am issue to think about in whatever is the specific situation prompting your question.