Impacted versions:
Master branch, should by 12.0

Steps to reproduce:
Install a third party addon with localization po file in i18n folder, even loading translation manually, the translation won't work, The console reports error: Translation .... not found in reference pot, skipping.
Reverse the change of  "odoo/tools/translate.py" in this commit, the issue was gone.

Expected behavior:
The po translation works as before.



""" Return the translation of the given XML/HTML node.
        :param callback: callback(text) returns translated text or None
        :param parse: parse(text) returns a node (text is unicode)
        :param serialize: serialize(node) returns unicode text
    """
    def nonspace(text):
        return bool(text) and not text.isspace()
    def concat(text1, text2):
        return text2 if text1 is None else text1 + (text2 or "")
    def append_content(node, source):
        """ Append the content of ``source`` node to ``node``. """
        if len(node):
            node[-1].tail = concat(node[-1].tail, source.text)
        else:
            node.text = concat(node.text, source.text)
        for child in source:
            node.append(child)
    def translate_text(text):