There is limited number of supported locales.

Google Chrome/Chromium/Vivaldi supports:
ar, am, bg, bn, ca, cs, da, de, el, en_GB, en_US, es, es_419, et, fa, fi, fil, fr, gu, he, hi, hr,
hu, id, it, ja, kn, ko, lt, lv, ml, mr, ms, nl, no, pl, pt_BR, pt_PT, ro, ru, sk, sl, sr, sv, sw,
ta, te, th, tr, uk, vi, zh_CN, zh_TW

Opera supports all Chromium locales and some more:
af, az, be, el, fr_CA, fy, gd, kk, me, mk, nb, nn, pa, zu

Opera does not support 'et' locale.

If you use an unsupported locale, browser will ignore it.

Up to date Chrome supported locales list:
https://developer.chrome.com/webstore/i18n?csw=1#localeTable
