There are words in some languages which are difficult to translate to other languages like gestalt in German.
There are words which get lost in translation without sufficient context.
It is possible that words from Hindu scriptures written in Sanskrit got mistranslated to English.
The word 'brahmacarya' got translated as celibacy. But it literally means 'to dwell on the divine'. The word 'varna' got translated as 'caste' - which has racial connotations - when it should have been 'class' or 'group'.
What is worse is that most Hindus learned from the incorrect translations to the extent that today even Hindus have misconceptions about what they are. I believe that a lot of misconceptions about Hinduism stems from these incorrect translations.
What according to you would be a significant mistranslated word/concept? A mistranslation that has caused the most damage or misconception to Hinduism.