Hi.
One of our customers run a multi language EPiServer CMS 5 R2 SP1 site (although the problem is identical in R2 SP2).
They also use LinkCollection in dynamic properties. It works great with languages that use a single part CustureInfo ID as 'en', 'no', 'de' etc. The multi-part CustureInfi ID languages does however not work.
When clicking the "AddLinkButton" button on the LinkCollection, an JavaScript exception occur.
The JavaScript function is named using the language ID and since the multi part ID's contain a hyphen ("-") it produces a faulty function name.

Exemples of this behaviour are:
LinkCollectionLaunchHyperlinkDialog_ctl00_FullRegion_MainRegion_EditForm_testen-US_ctl00
LinkCollectionLaunchHyperlinkDialog_ctl00_FullRegion_MainRegion_EditForm_testen-GB_ctl00

Also the performance of the dynamic properties edit page is catastrophic as with 17 active languages and all language unique properties rendered 17 times.
A nice solution would be to add a language select on the dynamic property edit page as to minimize the number of simultaneous controls rendered on the same page.

Cheers, Magnus