I finally had a couple of free minutes. I'm assuming you're using the Google Play version of the game.
Here's the link to a modified version: https://drive.google.com/file/d/18gVYhU ... Vjw1gK2TO/
To install, you have to enable installing from unknown sources: https://www.applivery.com/docs/troubles ... wn-sources
Then you have to download the language pack: https://drive.google.com/open?id=1IA0Ug ... JYU9zegOsH
I've already integrated your changes. You need to extract these on the Internal Storage, first create a directory called "bote" then extract there. I recommend using https://play.google.com/store/apps/deta ... lCommander to do this.
If all went well, you should be able to start the game now with the french version. If it crashes, the crashlog might tell you why (for example it looks for the "bote" directory in a different place etc.).
I hope it works, as every device is different (I only tested it on a Galaxy Note 4).
Great. Keep in mind that some strings are saved in save files so to test them you might need to start a new game (diplomacy messages, intel reports). But they should normally fit anyway so it shouldn't be a problem. Anyway now you can work directly with the fr directory and send me the results when done.