Just noticed this while using both Anki and Libre Office.
When the word เหนื่อย is printed in both Anki and Libre Office in noticed that mai eek can't be seen. It simply becomes part of sala eu.
With Libre Office I can highlight the word and select "Clear Direct Formatting" and the program will select a font that can display the vowel and tone mark correctly. Anki? Now sure what to do. Perhaps someone who is smarter than me with formatting within programs can offer a suggestion.
for the Thai language