This issue is applicable to languages using the Ethiopic script, but the principle probably also applies to a number of archaic scripts.

We are currently investigating whether there is really an issue here.

When underlining a word followed by an ethiopic wordspace, the punctuation should also receive the underline. (See the relevant section in the Ethiopic Layout Requirements doc.)

The CSS Text Decoration spec, Level 4 currently says that text-decoration-skip:spaces would not underline Ethiopic word spaces. This seems like a basic issue.

A test is available for this, but text-decoration-skip:spaces doesn't appear to be supported yet by browsers. The issue may arise when implementations begin to provide support for that value.