Customization menu does'nt work when I add a gt_cached.json file modify for french

[00Samada]

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Hi ! Firstly, thanks for all your work; it's a wonderful project.

I try to use FQM at the company where I work with my co-worker, and we want to improve the French translation. So, I dive into the gt_cached.json file and begin to change and re-translate some of the French translation. No offense, you did a great job, and French is not an easy language. We just want to improve the translation a little bit for us and our French-speaking friends around the world, if they want.

I modified the original gt_cached.json file and changed the lines of the French translation that I did not find good. When I was done, I checked the modified file with some online JSON parser. According to them, my file is okay. I even compare the modified file with the original to see if I didn't erase or change anything important. All is well at this point. But when I replace my file instead of the original file, I can't reach the "Customization" menu.

If you can help me solve the problem, I will be happy to share my French translation for FQM. I'll join the file I modified if anyone wants to look at it. gt_cached.modifie.json

To Reproduce
Steps to reproduce the issue:

1. cp the modified file to the original in the directory
2. down and up the docker with docker-compose
3. Go to the webpage of FQM
4. Click on the "Customization" menu in French "Personnalisation"
5. Wait until FQM brings me back to the home page with the error message : "[Error: something wrong , or the page is non-existing ]"

Please complete the following information:

• Debian 12 6.1.0-26-amd64
• Browser Chrome
• FQM Version [e.g. 0.9]

Error:
```2024-10-25 09:14:55.784692 ##### werkzeug.exceptions.InternalServerError: 500 Internal Server Error: The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the appl ication.``

Again, thanks for all your work, it's a great tool.