Sorry for lack of detail regarding this, but it's one of those things I done without really paying too much attention to what I was actually doing.
Basically, what I done was, went to try out the "Remember the user interface state" and then, I went to change some other options and noticed that the "Yes/No" 's had changed to something like "Ano/???" then I noticed the "Overview" tab text had changed, and it seemed when I changed view, ie went to the tasks view, all of the text changed (to czech I think!). Anyway, tried logging in/out etc... to no avail, eventually realised that my language was set to cs_cz.
What I imagine happened is, I went to the general preferences and for whatever reason it didnt read my langauges field so therefore didnt populate the field with "en_us" (or whatever numeric value it is in the database), and defaulted to the first one in the list (cs_cz), then when I saved, it overwrote my "en_us" with "cs_cz".
Just for reference, this was done quite soon after updating to 1.4.1.