One thing that I've always struggled w.r.t i18n is having to split messages up into often times less coherent chunks in order to add things like links or tooltips or styling elements in the middle of the text, which makes it more difficult to localize messages as a holistic piece independent of the source language. For a slightly contrived example to demonstrate this, let's say you have a string like this: "Please cl…
Another example is when you need to inject an image as a text decoration that includes text, or only makes sense in a particular part of the sentence.
One workaround I've considered is to add the decoration directly to the font you're using, so you can literally translate the decoration as text, but that doesn't usually feel like a reasonable solution, and still might not solve the problem for all languages.