[xsmasher]

I like to have a "double length" localization mode that doubles the English text; useful for fixing some layout issues while waiting for translations.

A separate toggle to underline everything going through the localization system (or adding some __delimiters__ around it if you don't support rich text) is great for spotting text that is not running through localization yet.

Once you have translations back, a "longest length" translation mode is more useful. It picks the longest translation for each token, no matter what the language. Confusing to look at, but great for seeing only the places where you actually have text-fit issues.

[WorldMaker]

Another tip I've found in pseudo-localization is to add in lots of emoji to the text. That can help check some Unicode assumptions/encoding issues in your localization pipelines in ways English readers can better visualize.