Hello there,
You may try to add the corresponding language packs for each package in the image, including the base Windows PE language pack.
For example, when you add the French (fr-fr) language pack to the base Windows PE image, and then to each of the optional components that are present in the default Windows RE image
You may refer to this detailed process:
Walkthrough: Create a Windows RE Image
http://technet.microsoft.com/en-us/library/dd744525(v=ws.10).aspx
Adding Languages
http://technet.microsoft.com/en-us/library/hh825125.aspx#BKMK_AddLanguagePacks
Similar discussion here https://answers.microsoft.com/en-us/windows/forum/all/windows-10-recovery-environment-language/b3ca490b-e72f-45c6-aa47-edf334f807d5
Hope this resolves your Query !!
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