1. Why not just continue to use your old skins? For the most part, skins have been upwardly compatible for a long time. In any event, to answer your question, we need a little more information. What does your [Extras] section look like in skin.conf?
2. The WeeWX applications work like any other Unix application: the date/time formats are set by the environment variable LANG. You didn't say what your value is for LANG, but I assume some European locale. To see what it is, use the locale command:
locale
You can override individual categories by using LC_xxx environment variables. For example, to use US style dates and times, you could use
LC_TIME=en_US.utf8 weewxd