It generally works for more than half the numbers on German websites, after setting Auto Country Prefix to +49. This needs more work for phone numbers with German style formatting. Here some examples which fail to dial the correct numbers:

+49 (0) 69 209 777 777 MeloSIP should drop the (0) in brackets.

08161/ 600 - 288 MeloSIP only dials +498161600, while dropping the 288

German websites use brackets or a slash to separate area codes and lots of spaces and dashes to make the numbers more readable. There are no strict rules for this, thus MeloSIP needs to interpret it as best as it can.

Some major sites do not show any clickable phone numbers, like the national phone directory dastelefonbuch.de

Here MeloSIP needs to add a feature to select and right-click for a ClickToDial context menu item.

I'm using it with the SIP client Bria 5.