Re: wHere to upload the MO file?
That directory doesn’t exist normally, it was discussed as a better solution to the usual plugins/buddypress/languages location due to overwriting
I think that page has been recently edited and I will track down the culprit and ask they edit and make things clearer, I wrote the Poedit section and at the time there was iirc clearer steps on file location alternatives.
For the moment try following the steps outlined saving the file in buddypress folder and editing your necessary files – the example code snippet that sets your language file to use – until clarification can be sought on new steps.