The ODEE says about breeches
Old English brēć (pl. only) [...] :- Common Germanic (except Gothic) *brōks, monosyllabic feminine. The further relations are obscure; some favour the early adoption of pre-Germanic *bhrāg- in Gaulish brāca, whence Latin brāca, bracca.
Pokorny claims that Gaulish brāca is a borrowing from Germanic, but doesn't deign to tell us what the Germanic word is.
brogue, which refers to a strong Irish accent and the shoes worn by people with strong Irish accents, is from Irish Gaelic bróg "shoe" from Old Irish bróc "trousers", borrowed from Old Norse brók (ODEE) or from Old English brōc, the singular of brēċ "breeches" (AHD). It seems these words are related to Gaulish brāca, but it's not clear how.