In the novel A Scanner Darkly, there were a number of passages containing German text. What did they say in English? Why weren't they in English like the rest of the book? I interpreted it to show that Bob Arctor was going crazy.
Translations of the German passages:
pages 175-6 (from Goethe):
You instruments, of course, can scorn and tease
With rollers, handles, cogs, and wheels:
I found the gate. you were to be the keys;
Although your webs are subtle, you cannot break
Why, hollow skull, do you grin like a faun?
Save that your brain, like mine, once in dismay
Searched for light day, but foundered in the heavy dawn
And, craving truth, went wretchedly astray.
I’m like the worm that burrows in the dust,
Who, as he makes of dust his meager meal,
Is crushed and buried by a wanderer’s heel.
Two souls, alas, are dwelling in my breast,
And one is striving to forsake its brother.
Unto the world in grossly loving zest,
With clinging tendrils, one adheres;
The other rises forcibly in quest
Of rarefied ancestral spheres.
Still this old dungeon, still a mole!
Cursed by this moldy walled-in hole
Where heaven’s lovely light must pass,
And lose its luster, through stained glass.
Confined with books, and every tome
Is gnawed by worms, covered in dust,
And on the walls...
Page 215 (from the Fidelio libretto):
How cold it is in this underground vault!
This is only natural; it is so deep.
Page 261 (from Heine):
I, unfortunate Atlas! A whole world,
A monstrous world of sorrows I must carry.
I bear a weight unbearable; a burden
That breaks the heart within me
As this is a short lyric poem the rest of it bears repeating:
Oh foolish heart, you have what you desired!
You would be happy, infinitely happy,
Or infinitely wretched, foolish heart.
And now– now you are wretched.
As for why those passages weren't in English: I believe your interpretation to be correct, as Bob started to loose grip on reality he began to drift into the past and remembered the German spoken in his house as a child (which was mentioned in the book).
According to Google Books,
Untitled poem reprinted from Heinrich Heine: Lyric Poems and Ballads, translated by Ernst Feise. Copyright 1961 by the University of Pittsburgh Press. Used by permission of the University of Pittsburgh Press. Other German quotes from Goethe's Faust, Part one, and from Beethoven's opera Fidelio.