Is there a limitation on submitting changes to tag descriptions for approval? I sometimes find the "Edit Tag Info" not visible. Is that a quirk or a restriction?
Any logged-in user can propose changes to tag descriptions (tag wikis and tag wiki excerpts). Except for users with more than 20k rep, the proposal (suggested edit) needs to be reviewed before it goes live.
There is one case where the tag wiki cannot be edited: if there is already a proposed change which is pending review. On a given tag wiki, only one proposal can be pending review at a time.
You may be temporarily prevented from suggesting edits if the review queue is full. There were a lot of suggested edits yesterday (thank you!), I didn't check the numbers but it's possible that the limit was reached at some point. The FAQ on the main meta also mentions a limit of 5 pending suggestion per person but I don't think that limit is currently active.
The tooltip on the grayed out “edit” button should tell you why you are unable to suggest an edit.