Translate all Text & Labels

Go to More > Languages menu item.

Now, to translate all the labels & text messages, you need to click the TRANSLATE icon under ACTION column of that individual language record. Check the following figure for reference.

Clicking this TRANSLATE icon will open a popup with a list of all the files to change those labels and text messages. Check the following screenshot for reference.

Now, click individual file and it will list all the labels given in that file to translate them in your newly added language. Check the following screenshot for reference.