I attended my friend's daughter's wedding last night. Just after saying Im Eshkachech and just prior to breaking the glass, the couple and all standing next to the chuppa recited Tehillim (Psalms) 128.
I know that my friend is Yekke. I assume that this may be a Yekke minhag, but, I don't know if this is unique to them or are others following this minhag, as well. What is the reason for this specific Psalm?
AFAIK, Im Eshkachech is a relatively recent addition. (As in, it only became popular since the founding of the State of Israel.) German communities have sung Tehillim 128 after the Kiddushin but before the breaking of the glass for centuries. We use the same tune as when we sing it Motzei Shabbos. It is either sung by 1, 3, or a group of individuals. (I have never heard of it being sung by the bride and groom themselves or by everyone around the Chuppah.)
As for why that specific Psalm - Google the translation. It is very apropos for a wedding ("Your wife will be as a fruitful vine", "may you see children [born] to your children").
http://www.chabad.org/library/bible_cdo/aid/16349/jewish/Chapter-128.htm
Source: I am a Yekke. This was done at my wedding and I (quietly) do this at every wedding I attend. Also, Shorshei Minhagei Ashkenaz has a chapter on this.
According to here there is a German minhag to sing/recite Tehillim 128 at the chuppah and also by Motza'ei Shabbos. If you look online there are many videos, mentions, etc. of the minhag. See here. The minhag is also briefly mentioned on the KAYJ Ashkenaz Forum.
I'm sure one of our local Yekkes here can verify whether this is true or not. You might also be interested in this question and its answers elsewhere on this site.
