The pending and welcome emails are both configured within CB > Configuration > Registration. This is has not changed from CB 1.x and is outlined in the CB 2.0 Primer and in our youtube videos below.
www.youtube.com/playlist?list=PLp0puRITgC7PuyzPsMUECDI46VE7IFSAX
You do not have to modify the language strings and can just adjust the parameters directly if you don't need multilingual usage.
WYSIWYG editors are intrusive and force their formatting onto the parameter. We use a textarea field in most places and directly support HTML in most places. Nothing is stripped from your input and nothing is modified on save. Try TinyMCE for example and you'll notice it forces its formatting and parsing onto your content; it's beyond frustrating to see tags stripped that you didn't expect or every linebreak forced into a paragraph format; all of which is the default WYSIWYG behavior that most don't even know how to turn off.
Modifying language strings right now requires modifying the language files, which we've explained in the CB 2.0 Primer in addition to our language page below. However, we will be adding an override feature for language plugins in a future release that lets you add override strings from backend without having to touch anything.
www.joomlapolis.com/cb-solutions/languages