This sounds off by an order of magnitude? Firefox's local translation models are only 20-70MB per language pair direction (e.g. en-to-fr or fr-to-en).[1] These models are also only released when they reach at least -5% of Google Translate's COMET score.[1] Currently Firefox ships with support for 32 xx-to-en language pairs and 29 en-to-xx language pairs.[1] As the number of language pairs increases, it probably isn't unreasonable for browsers to stop bundling every language pair and instead prompt users to download uncommon models the first time the user wants to use them.
Does the API trigger the download automatically, or does it ask for user permission?
(Answered my own question): Doesn't look like it requires the user's permission. Upon first use, the model will start downloading. The user has to wait for the download to finish before the API will work. That could take hours for 22gb.
Seems very backwards for markets where wired/wifi connections at home are nonexistant, 4g/5g is already unmetered and phones are the wifi you connect your devices to.
[1] https://mozilla.github.io/translations/firefox-models/