Make sure to disable Magento cache while working with the .csv translation. Otherwise, your changes will not be displayed instantly.
1. The default language of your Magento store is English. If you need to perform translation into any other language using your .csv file, simply go to the "en_US" directory (as it is shown below) and copy the file into the needed locale.
Find the needed extension .csv file below:
Magento Advanced Reviews and Reminders Extension
Magento Ajax Cart Extension
Magento Banner Pro Extension
Magento Cart Reservation Extension
Magento Checkout Success Extension
Magento Coming Soon and Maintenance Page Extension
Magento Estimated Delivery Date Extension
Magento Faves Extension
Magento Inspiration Wall Extension
Magento Invitations Extension
Magento Layered Navigation Extension
Magento Live Feed Extension
Magento Newsletter Popup Extension
Magento One Step Checkout Extension
Magento Order Status and Shipping Tracking Extension
Magento Popup Login Extension
Magento Private Sales & Flash Sales Extension
Magento Product Quick View Extension
Magento Recently Viewed Products Extension
Magento Reward Points Extension
Magento Search Autocomplete and Suggest Extension
Magento Shop by Brand Extension
Magento Social Login Pro Extension
Magento Twitter and Facebook Login Extension
Magento Who Bought This Also Bought
2. As an example we will show how to perform German translation of the .csv file here. Please, check an example of the path to the German locale where we have copied the .csv file to be translated.
Where "Plumrocket_NAME" is the name of your extension which can be found above.
3. Open the "de_De/Plumrocket_NAME.csv" file using any text editor (e.g. Notepad++) and translate the second phrase of each string.
All the strings in your .csv file should start and end with double quotes and should be separated with comma [,]
The translated text should look like this:
"Add to Cart", "Translated Text"
Please, check an example of translation into German:
"Add to Cart", "In den Warenkorb"
For more details on how to edit .csv files during the translation, please read here.