I got the info from the census, some of which you can look at for free at labs.familysearch.org and Ancestry.com. For those you cannot see for free I suggest checking with your local libraries to see if they have Ancestry or Heritage Quest.
The 1910 census that includes Jane seems to show her with the same data for Susan. It could even be Susan, it isn't easy to read. The number of years married and both only married once makes me feel it is not his second wife.
I could not find any connection to Pennsylvania or a second wife. But again I'm assuming it's the same Mathew Sanders. It would seem to be from what I can tell.
He may well have spoken German as people in those areas of Europe often spoke more than one language, one at home and the other in business or work.
According to the Montana State Archives website they have the local naturalization papers for that state.