This is "kind of" a bug. The gettext() redirection for "footnote1", et al., goes to the text in the locale files. If you don't have a "lang" specified, then it doesn't know where to go, so no replacement is done: you see "footnote1", "footnote2", etc.
To fix, specify a "lang":
[[Defaults]]
# Which language to use for all reports. Not all skins support all languages.
# You can override this for individual reports.
lang = en
The assumption was that if a user upgraded, then s/he would have the old Standard skin, so the old version of weewx.conf would work. OTOH, if a brand-new install is done, then the new version of the Standard skin would be installed, along with a new version of weewx.conf, which includes the "lang" specification. I would guess that you upgraded, but replaced "Standard" with the new version.
Having said this, it really should default to something better. The right thing to do is what the Seasons skin does: instead of using "footnote1", etc., as the key, use the actual English string.
-tk