"...despite Mark Twain's vicious rant,"

I don't believe Mark Twain's Appendix D is vicious nor a rant. In fact, it is a brilliant piece of humorous writing in its own right and I would give a great deal to be able to write and communicate as well as that. Furthermore, having worked in both Austria and Germany I've known several native German speakers who are fluent in English and who laughed themselves almost hoarse after I brought it to their attention. They weren't a bit offended by it, they then pointed to the many peculiar idiosyncrasies of English and said that in any competition for same then English would likely be the winner. (BTW, you'll even find native German speakers reading The Awful German Language on Project Gutenberg.)

Moreover, I learned more about the German language from Twain's writing than I ever did from the equivalent number of words in any German language textbook written in English. Clearly, I cannot do justice in the space or time available but let me mention a few instances.

"These things are called "separable verbs." The German grammar is blistered all over with separable verbs; and the wider the two portions of one of them are spread apart, the better the author of the crime is pleased with his performance."

The 'REISTE AB'/'departed' example that Twain quotes is both humorous and very memorable: "The trunks being now ready, he DE- after kissing his mother <...> <...> ...more dearly than life itself, PARTED." After reading this it's almost impossible for someone who is learning the language to ever let separable verbs pass them by without noticing them.

"These things are not words, they are alphabetical processions."

Of course, they are. And as Twain points out they also possess 'perspective'—and many native German speakers would agree with this assessment, in fact some are quite bemused by the fact that their language has the world's longest words.

"<...> Of course when one of these grand mountain ranges goes stretching across the printed page, it adorns and ennobles that literary landscape—but at the same time it is a great distress to the new student, for it blocks up his way; he cannot crawl under it, or climb over it, or tunnel through it. So he resorts to the dictionary for help, but there is no help there."

Not only is this wonderfully descriptive prose but it's in fact true. To prove the point, here are a few more that are not included in Twain's text:

Rechtsschutzversicherungsgesellschaften

Donaudampfschiffahrtsgesellschaftskapitän

Betäubungsmittelverschreibungsverordnung

Bezirksschornsteinfegermeister

Donaudampfschiffahrtselektrizitätenhauptbetriebswerkbauunterbeamtengesellschaft

Whew, that's 79 or 80 letters depending on which spelling one uses.

"One cannot overestimate the usefulness of SCHLAG and ZUG."

That's very true, and so are very useful (and somewhat tiny) words such as zu, bis and nach — that is, once one gets to understand their German nuances (initially their usage can be confusing—at least I found them to be so given that to, till and until in English are used in a somewhat less prescriptive way.

"The Germans do not seem to be afraid to repeat a word when it is the right one. They repeat it several times, if they choose."

Until I read this passage, it was never evident to me that we native English speakers actually go out of our way to avoid word repetition.

"In the daybeforeyesterdayshortlyaftereleveno'clock Night, the inthistownstandingtavern called 'The Wagoner' was downburnt. When the fire to the onthedownburninghouseresting Stork's Nest reached, flew the parent Storks away. But when the bytheraging, firesurrounded Nest ITSELF caught Fire, straightway plunged the quickreturning Mother-Stork into the Flames and died, her Wings over her young ones outspread."

Even the cumbersome German construction is not able to take the pathos out of that picture--indeed, it somehow seems to strengthen it. This item is dated away back yonder months ago. I could have used it sooner, but I was waiting to hear from the Father-stork. I am still waiting.

There are some German words which are singularly and powerfully effective. For instance, those which describe lowly, peaceful, and affectionate home life; those which deal with love, in any and all forms, from mere kindly feeling and honest good will toward the passing stranger, clear up to courtship; those which deal with outdoor Nature, in its softest and loveliest aspects—with meadows and forests, and birds and flowers, the fragrance and sunshine of summer, and the moonlight of peaceful winter nights; in a word, those which deal with any and all forms of rest, repose, and peace; those also which deal with the creatures and marvels of fairyland; and lastly and chiefly, in those words which express pathos, is the language surpassingly rich and affective. There are German songs which can make a stranger to the language cry. That shows that the sound of the words is correct—it interprets the meanings with truth and with exactness; and so the ear is informed, and through the ear, the heart."

With these wonderfully perceptive words, Twain not only shows us what a master he is at conveying his message but also that he is an acute observer of human nature. It is also indicative that his knowledge and fluency of German is higher than one may gather at first glance. Here, I can attest to the validity of what Twain says in respect of these German words. For instance, Schubert's remarkable song cycles Die schöne Müllerin (The Fair Maid of the Mill) and Die Winterreise ([the] Winter Journey) often reduce me to tears. Also, I find the pathos and heartfelt meaning of these words abundantly evident whenever I wander though a German Friedhof (cemetery). These powerful and yet unusually simple German words stare back from nearly every Grabstein if so as to remind one of one's own mortality.