From the information you provided, it appears that the Rest API is not working for French users when the term is in French (Litige et résolution de conflits), but it works when the term is in English (Litigation and Dispute Resolution).
Rest API is language-independent, particularly when dealing with lists and libraries. Everything works fine when the site is in English and the user's language is English, but many things don't work like the example when the Rest API encounters a different language.
You need to encode your query component with a different language. You could use any online tool to encode.
Reference:
https://blog.icefire.ca/blogs/post/how-to-make-sharepoint-api-calls-language-independent
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.