This guide provides instructions for localizing an OLED display by creating custom fonts, updating relevant code files, and defining language settings. The localization process involves the following steps:
### 1. Create an Extended ASCII Custom Font
Use a glyph editor to create a new font file. The easiest way is to use the online [glyph editor](https://rawgit.com/ThingPulse/esp8266-oled-ssd1306/master/resources/glyphEditor.html) from the OLED library ([glyph editor source code](https://github.com/ThingPulse/esp8266-oled-ssd1306/tree/master/resources)).
1. Copy and paste the existing font.
2. Modify it according to the desired codepage and save the new font file in the `graphics/font` folder.
_Note: The font file format differs from the common Adafruit GFX format._
### 2. Update the `customFontTableLookup` Function in `Screen.h`
1. Map the double-byte UTF-8 code to the corresponding extended ASCII character of the desired codepage by updating the `customFontTableLookup` function in the `Screen.h` file.
2. Modify the `switch (last)` statement: Use the left byte from the UTF-8 code in the `case` label to map the character's right byte to its extended ASCII code by specifying an offset.
### 3. Define Language and Font in `Screen.cpp`
Add language-specific font definitions using conditional compilation:
```c
#ifdef OLED_{LANG_NAME}
#include "fonts/OLEDDisplayFonts{LANG_NAME}.h"
#endif
...
#ifdef OLED_{LANG_NAME}
#define FONT_SMALL ArialMT_Plain_10_{LANG_NAME}
#else
#define FONT_SMALL ArialMT_Plain_10
#endif
```
### 4. Configure Language Settings
#### Primary Method: Define in `variant/*/platformio.ini`
Language settings can be defined in the `platformio.ini` file under the appropriate variant directory:
```text
build_flags =
${esp32_base.build_flags}
-D xxxxx
-D OLED_{LANG_NAME}
-I variants/xxxxx
```
#### Alternative: Define in `userPrefs.h`
As an alternative to modifying `platformio.ini`, the language can be defined in `userPrefs.h`.
```c
#define OLED_{LANG_NAME}
```
Both methods achieve the same result, and the choice depends on the specific project setup.
