ImageGenerator: ignore the duplicate locales

Some language variants have the duplicated translations. Therefore,
we can compare the translated string for each locale to the default
text string for that language. And the duplicated ones will be skipped
to save some space.

Bug: 74397117
Test: generate and check the image
Change-Id: If51fa8fe700350c06f084f0e74d3698b82d6f177