Tokens (markers that are replaced at run-time by other text or values) in strings can be the bane of a translator’s life if used incorrectly because they frustrate a correct translation being made. However, I love the way that the Facebook translation tool allows you to comment on their use as you translate. 

Looking at the options below for commenting on token use is an education in itself (the tokens concerned are {number} and {chat-service-name}).

This approach allows users to comment as much on the effectiveness of the internationalization (i18n) practice as on the quality of the translation.

Facebook’s internationalization best practices for developers are here.