Help Needed in Understanding linkage between the Fonts and English Text Only in InDesign IDML Files

My goal is to translate the original InDesign (.indd) file from English to Japanese only. For this, I’m following the approach below:
1. Export the InDesign file to IDML format, which is structured and editable.
2. Use Python code to translate the english text and update its font and language (so the translated text is properly displayed).

Note: I only want to translate English text and update its font and language.

However, the InDesign files are a bit complex, as they contain both English and Arabic text side by side. When processing the IDML file with code, the English content is translated correctly without affecting the Arabic text. But when updating fonts, either all text—including Arabic—gets updated, or some English text fonts remain unchanged.

Therefore, I need help understanding how fonts and languages are linked to text in InDesign IDML file, so I can update the font and language for English text only.