Allow to change the language in the backend

[lucasiscovici]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] Browser language dependant

Describe the solution you'd like Allow to change the language in the backend (config)

Describe alternatives you've considered dirty hack

original_config_load_translation = cl.config.load_translation
cl.config.load_translation = lambda _: original_config_load_translation("fr-FR")