Thanks for the idea @Kurniawan, this is along the lines of https://connect.mozilla.org/t5/ideas/have-the-possibility-to-make-a-feedback-about-a-wrong/idi-p/44205, which we have started investigating. You idea would also allow us to crowdsource sample...
@graviton the feature is usable by opening the "about:translations" page. We have recently made various improvements to this page, and we are currently working on making it even better and on making it more discoverable.
@Ignacio-LR if you're interested in helping out, feel free to join the Firefox Translations channel on Matrix (https://chat.mozilla.org/#/room/#firefoxtranslations:mozilla.org). We would be happy to have your help to introduce Romansh support!