Feature request: let the user pick which language packs get flashed

[winst0niuss]

Feature request: let the user pick which language packs get flashed

Problem

Every build ships all 33 languages, but a user only ever reads one or two. The translation tables are a fixed cost in an app partition that is already close to full, and that space is what new features have to fit into. They are also paid twice, once in each OTA slot.

Proposed solution

Add a Language Options block to the flasher UI: a checkbox list of the available languages, defaulted to English plus the browser locale. The user ticks the ones they want and the flasher writes an image containing only those.

The reference model is the Betaflight Configurator flasher, where the user picks features before the image is written to their board.

User flow

1. User connects the device to the flasher.
2. The flasher shows a Language Options section.
3. User ticks one or more languages (English always on — it is the fallback for missing keys).
4. The flasher flashes the firmware plus the selected locales.
5. Settings → Language then lists exactly those entries.

[winst0niuss]

A way to do this without a build server: keep the strings out of the firmware and put them in their own flash partition.
There's already spiffs in partitions.csv sitting unused (3.375 MB, nothing mounts it), so a chunk of that would do. ESP32 can map a partition into memory space directly, so I18n::get() still just returns a pointer into flash and RAM usage stays at zero.

Then the flasher builds nothing - it writes the same firmware for everyone plus a small file with the selected languages, and changing languages later only means rewriting that file.

[winst0niuss]

@itsthisjustin, @Uri-Tauber, what do you think about this?

[Uri-Tauber]

I'm against having multiple builds.
Debugging user complains is already hard enough. Having different build will double that.

That said, moving assets to SPIFFS is something we already discussed before. It's on my mental todo list, with hyphenation at the head of the list.
German hyphenation alone costs us ~200kb, almost 70% all the languages strings together.

Ultimately, I think hyphenation assets should be downloadable like SD fonts and get stored on SPIFFS, those freeing up a lot of space and letting us add hyphenation for a lot more languages.