The forums are not Scirra's support. To question the support itself, do so by sending an email to where you'll get official answers and where google translate will be used.
The forums are a different service, having purchased Construct does not give any special rights of use or of behavior in the forums to the users paying or not.
English is used as an international language (as well as Scirra's main language).
Items are checked for approval every business day. There are no "minimum", it is your choice what you sell and at what price.
Depending on the quality of your items and what is available on the market, you can see if it makes sense and if it will sell.
To provide and make commercial usage of game templates (made in Construct 2) though, you need to own a valid license for Construct 2.
As per the licensing terms, you cannot use the free edition to sell templates.