Problem/Motivation
When creating a link field, the optional help text for the field is not rendered. Instead, there are string constants that are displayed based off of the type of url the field expects (internal vs external). I don't know of other examples where Drupal is prescriptive on the language used for a field, but it makes sense to me that if I provide help text; it should be displayed instead of the default, 'This must be...'.
Also, I understand that there may be a theming solutions for this problem. If that is the preferred fix, I think there needs to be more documentation on how to correctly implement it and the help text for the field should warn authors, e.g "this behaves differently than you might expect".
Note: The attached patch file is the output of a linux diff in which I had to have two copies of the file (LinkWidgetBU.php and LinkWidget.php). If necessary, I can provide a git version.
Proposed resolution
Check if a content author has provided help text for link field, if so , use it.