Unless you want this to work even for !git builds I'd really advise that you get attempt to find the git remote URL and use Project.from_repo_url to resolve that into a Project. from_xpath is slower and less reliable than from_repo_url.

2 space indentation for new code please.

These additions are missing a test case :P

Bunch of style problems here. TLDR code I want at the bottom.

Dir.pwd + modifier if (when the line doesn't exceed 80 chars) + unless is preferred for style reasons (https://github.com/bbatsov/ruby-style-guide)

i.e.

target = "#{Dir.pwd}/#{srcdir}/po" unless target

That said, instead of expanding with Dir.pwd manually you'd want to File.expand_path("#{srcdir}/po"). If srcdir is already an absolute path it will append /po, if it is not it will be turned into an absolute path relative to pwd whilest also expanding ~ correctly http://ruby-doc.org/core-2.4.0/File.html#method-c-expand_path

Also, in ruby, method params are evaluated as they appear, so since target is after srcdir you can already deref srcdir.

Putting everything together this can be expressed in the method definition without any if:

def get(srcdir, target = File.expand_path("#{srcdir}/po"),
        allow_edit = true)

I think the ifs here need to be moved inside out.

if has_translations
   cmakeappendcrap if allow_edit
else
   Dir.delete('po')
end

(allow_edit shouldn't have an impact on cleaning up the dangling po dir)

File.expand_path

def get(srcdir, target = File.expand_path("#{srcdir}/po"),
            allow_edit = true)