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M doc/i18n.md

@@ 66,7 66,50 @@ Definition for every key code used in the phone is in [the key_codes.hpp file (K
 
 ### Date and time
 
-MuditaOS follows [Linux `date`](https://man7.org/linux/man-pages/man1/date.1.html) to format date and time. 
+MuditaOS follows [Linux `date`](https://man7.org/linux/man-pages/man1/date.1.html) to format date and time.
+
+## Font conversion
+
+MuditaOS doesn't have built-in support for ttf/otf fonts, so we generate bitmap files for fonts. The official release uses GT Pressura Typeface which is a licensed font ([more info](../LICENSE.md))
+
+MuditaOS supports the following languages (and characters) out-of-the-box:
+
+- English
+- German 
+- Spanish 
+- Polish
+- French
+
+For other languages there might be a need to add language-specific glyphs, build them using [fontbuilder](https://github.com/mudita/fontbuilder) and add them to the repository.
+
+[Here's a list of glyphs that are supported by GT Pressura](https://www.grillitype.com/api/storage/app/uploads/public/5b6/c52/16b/5b6c5216b40a8675629257.pdf) (our current license covers only the Latin alphapbet characters).
+
+[Here's a list of characters currently added to the build](https://github.com/mudita/fontbuilder/blob/master/charset.txt).
+
+If your characters aren't currently supported please know that we're working on adding a fallback font inside MuditaOS that would enable to render the UI in more languages without the need of using proprietary typefaces.
+
+### Adding glyphs
+
+We use [fontbuilder](https://github.com/mudita/fontbuilder). It has font sets saved in files. This is not the best solution to store system presets (we should rather have it in release process). In order to do this:
+
+- feed FontBuilder headless run with preset file and build MPF (Mudita Pure Font)
+- put these fonts in build folder
+
+On Mudita Pure phone we use:
+
+- default font (`gt_pressura` font family)
+- fallback font (other font with all characters available)
+
+`▯` ← indicates when there is no glyph for a unicode character in current font
+
+#### Naming convention
+
+It’s a good practice not to rename font names - these are stored in font metadata too and metadata is used in code (**not the font file name**). Please just keep names as they are.
+
+#### Where are the files?
+
+- Source font files used for the build: `PurePhone/image/assets/fonts/`
+- Font files used at runtime (copied upon build): `PurePhone/<build_folder>/assets/fonts/`
 
 ## How to start localizing the interface