Katharina Schuhmann 

I can't be 100% on this but, I think this might be occurring because the font you mapped doesn’t actually support Chinese characters, or the mapping didn’t apply as expected.  Trados only swaps the font name in the IDML; it doesn’t ensure the new font has the right glyphs.  When InDesign opens it, you get boxes because it’s still referencing a Western font.

This article might he helpful as I think this is more of an InDesign issue than a Trados one: https://community.adobe.com/t5/indesign-discussions/native-american-symbols-displaying-as-squares/m-p/12858168

In short: check that Microsoft YaHei is installed, make sure the mapping matches exactly, and confirm the IDML actually uses that font when opened in a text editor.

Katharina Schuhmann 

I can't be 100% on this but, I think this might be occurring because the font you mapped doesn’t actually support Chinese characters, or the mapping didn’t apply as expected.  Trados only swaps the font name in the IDML; it doesn’t ensure the new font has the right glyphs.  When InDesign opens it, you get boxes because it’s still referencing a Western font.

This article might he helpful as I think this is more of an InDesign issue than a Trados one: https://community.adobe.com/t5/indesign-discussions/native-american-symbols-displaying-as-squares/m-p/12858168

In short: check that Microsoft YaHei is installed, make sure the mapping matches exactly, and confirm the IDML actually uses that font when opened in a text editor.