All filter messages have a description by now:

'articlefeedbackv5-special-filter-all' => 'Shows all records, including ones that have been oversighted (deleted) by an oversighter or hidden by a monitor.',
'articlefeedbackv5-special-filter-notdeleted' => 'Show all records that have not been oversighted',
'articlefeedbackv5-special-filter-comment' => 'Feedback with text comments',
'articlefeedbackv5-special-filter-relevant' => 'Feedback with the highest relevance score',
'articlefeedbackv5-special-filter-abusive' => 'Feedback that has been marked as abusive',
'articlefeedbackv5-special-filter-helpful' => 'Feedback that has been marked as helpful',
'articlefeedbackv5-special-filter-unhelpful' => 'Feedback that has been marked as unhelpful',
'articlefeedbackv5-special-filter-requested' => 'Feedback that has been requested for oversight',
'articlefeedbackv5-special-filter-unrequested' => 'Feedback that has been unrequested for oversight',
'articlefeedbackv5-special-filter-visible' => 'Feedback that has not been hidden',
'articlefeedbackv5-special-filter-hidden' => 'Feedback that has been hidden',
'articlefeedbackv5-special-filter-oversighted' => 'Feedback that has been oversighted',
'articlefeedbackv5-special-filter-unoversighted' => 'Feedback that has been un-oversighted',
'articlefeedbackv5-special-filter-declined' => 'Feedback where the oversight request has been declined',
'articlefeedbackv5-special-filter-unhidden' => 'Feedback that has been un-hidden',
'articlefeedbackv5-special-filter-featured' => 'Feedback that has been featured',
'articlefeedbackv5-special-filter-unfeatured' => 'Feedback that has been un-featured',
'articlefeedbackv5-special-filter-resolved' => 'Feedback that has been resolved',
'articlefeedbackv5-special-filter-unresolved' => 'Feedback that has been un-resolved',
'articlefeedbackv5-special-filter-all-watchlist' => 'Shows all records, including ones that have been oversighted (deleted) by an oversighter or hidden by a monitor, when viewing items on watchlist = without totals',

It's debatable if repeating the possibly hard to translate words like (un)oversight, unfeature, unrequest and "highest relevance score" are sufficient context to allow translation without additional questions.

Improved docs (upon closer inspection, param documentation was missing as well): https://gerrit.wikimedia.org/r/#/c/38293/

'Feedback that has been un-resolved',
'Feedback that has been un-oversighted',

Not totally clear - Has the feedback been without resolution/oversight since it was reported, or does this refer to a status change from resolved to unresolved resp. oversighted to un-oversighted? In some of my languages this makes a difference for translating.

And I agree that "unfeature" is rather untranslatable into some languages without using three or four words.

Gerrit 38293 improves the situation a lot. Thanks for that.