If you use a theme or plugin that was coded in a language other than English, you may notice that the source language in the String Translation page is incorrect. To fix this, you can change the source language of your strings.
To change the source language of specific strings, select them and click on the Change language of selected strings button. Then, select the new language.
You can also change the language of entire contexts. This is useful when you get a theme or a plugin, that’s coded in a language other than English. Click on the new link, at the top of the String Translation page, Language of domains.
Then, choose the new language.
The page will show you a table of the strings in that domain. You can choose the new language and also make it the default language for new strings that will be added to that domain.