Central/Eastern European (CE) national character support for embedded displays

[stachuman]

Adds Central/Eastern European (CE) national character support for embedded displays using the Adafruit GFX 5x7 bitmap font.
Characters like Ą, Č, Ž, ß are rendered natively instead of being replaced with block characters.

What changed

• New file: tools/generate_5x7_font.py — Python script that generates custom 5x7 font glyphs by compositing base CP437 letters with accent overlays (cedilla, ogonek, caron, acute, etc.)
• New file: src/helpers/ui/locale_font.h — Generated header containing a replacement font[] array (105 national characters) and a mapCodepointToSlot() function for UTF-8 → font slot mapping
• Modified: src/helpers/ui/DisplayDriver.h — translateUTF8ToBlocks() now decodes UTF-8 and maps codepoints to custom font slots when LOCALE_CE is defined
• Modified: platformio.ini — Added -include src/helpers/ui/locale_font.h to base build flags
• Modified: src/helpers/ui/E213Display.cpp, E290Display.cpp — Added cp437(true) to fix character rendering for slots >= 0xB0

Covered displays

• SSD1306Display (OLED 128x64, e.g. Heltec V3/V4)
• SH1106Display (OLED 128x64, e.g. Heltec V2)
• ST7735Display (TFT, e.g. Heltec T114)
• ST7789LCDDisplay (TFT, e.g. Heltec V4 TFT, T-Beam)
• E213Display (E-ink 2.13", e.g. Wireless Paper, Vision Master)
• E290Display (E-ink 2.9", e.g. Vision Master E290)

Supported languages

Polish, Czech, Slovak, Hungarian, Romanian, Croatian, Serbian (Latin), Slovenian, Bosnian, Turkish, Lithuanian, Latvian, Estonian, German (ß), and other languages using Latin-1 accented characters (French, Spanish, Portuguese, Italian, etc.)

How to use

Add -DLOCALE_CE to your build flags:

In your variant's platformio.ini:

build_flags =
${some_base.build_flags}
-DLOCALE_CE

Or pass it via environment variable:

PLATFORMIO_BUILD_FLAGS="-DLOCALE_CE" pio run -e your_target
When LOCALE_CE is not defined, behavior is completely unchanged — the original CP437 font loads as before.

How it works

The custom locale_font.h defines the FONT5X7_H header guard before Adafruit GFX's glcdfont.c is included, causing the original font to be skipped. The replacement font keeps ASCII (0x00-0x7F) identical to CP437 and places national characters in the 0x80+ slots. No display driver rendering code is changed — only the font data and UTF-8 translation function.