Hi Lilriv,
If your Battle.net account already is at the limit of WOW accounts then I fear that you’ll not be able to use that battle.net account to directly post on the US forums. There is nothing stopping you making a 2nd battle.net account for US WOW forums if you really wish to post there.
Sadly there is currently no way that the WOW account limit for Battle.net can be bypassed 