Laßt uns alle fröhlich sein,preisen Gott, den Herren,der sein liebes Söhneleinuns selbst thut verehren.Er kommt in das Jammerthal,wird ein Knecht auf Erden,damit wir im Himmelssalgroße Herren werden.Er wird arm, wir werden reich,ist das nicht ein Wunder?Drum lobt Gott im Himmelreichallzeit, wie jetzunder.O Herr Christ, nimm unser warhdurch dein heilgen Namen;gib uns ein gut neues Jahr,wers begehrt, sprach: Amen.Urban Langhanns, um 1560.
My prose translation:
Let us all be cheerful,Praise God, the LordWho even His dear SonGives to us.He comes into the vale of tears,Becomes a servant on earth,So that we in Heaven's hallBecome great lords.He becomes poor, we become rich,Is that not a wonder?Therefore praise God in HeavenAlways as now.O Lord Christ, protect usThrough Your holy name;Give us a good new year,He who desires it, say: Amen.Urban Langhanns, around 1560.
I took "selbst" in the first verse as an adverb, not a reflexive pronoun. It's a bit unclear though what exactly it's modifying. I pulled it forward a bit so that it modifies "sein liebes Söhnelein" (His dear Son).
Part of the second verse comes from Philippians 2:7: "but made himself nothing, taking the form of a servant, being born in the likeness of men."
I'm not too confident in my translation of "allzeit, wie jetzunder" as "always as now."
This hymn appears as "Let Us All with Gladsome Voice" in The Lutheran Hymnal (#97), Lutheran Worship (#42), and The Lutheran Service Book (#390). In all of these, and as the Gesangbuch notes, the text is sung to "its own melody." Here's the TLH arrangement: