Add FR translation of messages

[cregouby]

library(safetensors)
Sys.setLanguage("fr")
safe_save_file(list(x = torch::torch_randn(10, 10), x = torch::torch_randn(10, 10)))
#> Error in `safe_save_file()`:
#> ! Les noms dupliqués ne sont pas autorisés dans la liste `tensors`

^{Created on 2024-09-06 with reprex v2.1.1}