You could always send whoever it is a Battlenet Friend request, then you can chat to each other on the launcher’s chat, even if you play on a different region.
Member = Trust Level 2
Regular = Trust Level 3
The whitelist of sites that TL2 are allowed to embed is very limited, i.e. whereby you can put the item into the post itself. YouTube videos are one such allowed thing.
However, for creating clickable links, for TL2 posters that’s restricted to Blizzard owned domains, I believe, i.e. at TL2 you can create clickable links to Blizzard’s blogs, game guide, armoury pages and so on.
To create clickable links to non-Blizzard domains, or to embed pictures, requires TL3.
There’s a pinned thread…
…but the values specified within it, whilst correct at the time of publishing, are no longer valid. For example, you can get to TL3 with a much, much lower total of posts / threads read than is specified there (it’s more like 3000 than 20,000 now). Also, the requirement for Likes Given is not a reach and forget target, it’s a minimum of 30 likes, and that needs to be maintained over a rolling 90 day period.