A note is not welcome on the Startup page, please see https://josm.openstreetmap.de/wiki/StartupPageSource?action=diff&version=2512&old_version=2511

The online translation server is mostly overloaded. Several bug reports about this issue exist.

It is recommended to use an offline translation tool like https://omegat.org/. Its fast regex search over translation and source gives the change to maintain a consistent translation. All online tools (Transifex too!) are lacking on this task.

The reasons behind and the way up to en_CA are shown on https://josm.openstreetmap.de/ticket/17380#comment:14