Translate add-on helps you create your personal vocabulary. Type words and phrases in one column, the translations will appear in the column next to it.
To start, choose languages in "Add-ons > Translate > Choose languages". The add-on will start watching changes in the spreadsheet. As soon as you edit a cell its translation to the target language will appear in the cell next to it.
You can also translate a selection by selecting a range, then choosing "Add-ons > Translate > Translate selection".
The add-on needs access to your spreadsheet to translate text in it. It doesn't store data from your spreadsheets or send any of the data to a third party.
For issues and questions visit add-on's Google group.