Add language en-us
I propose adding support for English as spoken in the United States (en-us). Currently, there is support for en-ca and en-gb. I understand that en is assumed to be U.S. English but don't think it needs to be this way. The default English (en) used in Blockly is non-US English (using "colour"), and we find it useful to maintain a U.S. English translation (en-us) (using "color").
We can map it as such for your product. Here, en is assumed to be enUS.