Run same test suites on multiple languages (localization)

I'm new to testing world and i'm using testNG. I have a test suite with a few classes as below:

- LoginTest
- SignUpTest
...

Our website supports 2 languages and both localized sites are identical (except the localized strings). The way I setup my project is that I have 2 packages: English and Japanese which contain all the same test classes as above but validate against diffrent strings. I.e:

com.web.test.English
-- LoginTest
-- SignUpTest
-- EnglishStrings.json
com.web.test.Japanese
- LoginTest
- SignUpTest
- JapaneseStrings.json

Now, whenever the login page or signup page changes, I need to update the locator and validation methods in both English and Japanese package. Is there any neat and faster way to make each test class run twice with both EnglishStrings.json and JapaneseString.json? Thank you.