There is a way to extract the subtitles from an .mkv file, translate them using online translation tool and then add the new translated substiles to the .mkv file

Download these tools:

mkvtoolnix – MKVToolNix download latest version (fosshub.com)

gMKVExtractGUI – https://sourceforge.net/projects/gmkvextractgui/

Use gMKVExtractGUI to extract the existing subtitles from the .mkv file. The program depends on mkvtoolnix and you have to specify where it is installed.

Use the (Subtitles Translator – Free Online Subtitle Translator to translate the extracted subtitles to a different language of your choice.

Use mkvtoolnix to merge the translated subtitles into the .mkv file. It will create a new .mkv file