good vs. well
This is the almost classic error of confusion between the adjective good and its adverbial counterpart well–common among native English speakers as well as among learners, though good for well is still considered substandard. There are two factors which tend to increase the confusion between good and well. One is the use of good as an adjective complement after verbs like feel, look, smell, sound, and taste, e.g.:
I feel good.
Your idea sounds good.
The meat smells good.
Due probably to misleading grammatical explanations in school, many native speakers have the idea that good after these verbs is an exception to the rule that good is used as an adjective. This is entirely wrong, of course, since these verbs require adjective complements, not adverbs, just as the more typical copulas before or become:
I am/feel tired/*tiredly.
Your idea is/sounds wonderful/*wonderfully
The meat is/smells delicious/*deliciously
The real exceptions are the cases where adverbial forms are used with these verbs, as in
I feel badly about it.
Dogs smell more sensitively than humans.
Here the meanings of the verbs are different, however. Feel badly can refer only to emotional feeling, whereas feel bad can mean this or physical discomfort. Smell in the second sentence refers not to the odor, of dogs but to their ability to smell. The second confusing factor regarding good and well is the use of well as an adjective meaning 'healthy.' Thus sentences like She doesn't feel/sound/look well today are perfectly correct in this sense. Some native speakers, though, having taken great pains to learn that good is an adjective and cannot be used in sentences like
He sings real good (substandard)
will overgeneralize this rule and apply it to verbs like feel, look, etc., assuming He feels good is also wrong (which it is not) and thus producing sentences. like
*I feel well about the fact that I was able to help.
*That really tasted well.
*You're looking very well this morning.
The first two sentences would be recognized as incorrect and obvious hypercorrections by many educated speakers. The use of well referring to appearance with look is somewhat more acceptable, but cannot be considered recommended usage.
once vs. someday
Once is used as an adverb to mean 'on one (as opposed to two, three, etc.) occasions or 'sometime in the (indefinite) past,' e.g.:
I'm only going to do it once.
He was once a rich man, but now he's destitute.
It is also used as a conjunction to introduce temporal clauses, meaning 'as soon as, from the moment that':
Once you give in, he'll take advantage of you.
The second meaning of once is parallel to the use of someday meaning 'sometime in the indefinite future,' which is probably the source of confusion in (1)-(2). Compare:
Once he was a rich man.
Someday he'll be a rich man.
In German, furthermore, einst can be used in both senses:
Er war einst ein reicher Mann.
Er wird ein8t ein reicher Mann sein.
at most vs. most
At (the) most means 'not more than.' e.g.:
He's thirty at (the) most.
(The) most, on the other hand, as used in (1), is the superlative of a lot. Compare:
Fasching is celebrated a little (bit)/more/a lot/(the) most in
Cologne.
for a long time vs. one time, two times, etc.
For followed by a noun phrase denoting a period of time expresses duration–the time period during which something takes place, or, in negative sentences, does not take place. In affirmative sentences for can be omitted:
I thought about it (for) a long time/three hours,, etc.
but
I haven't thought about it for a long time/three hours, etc.
When referring to the repetition of an event rather than its duration, a cardinal number or a quantifying adjective followed by times is the appropriate expression (cf. (1)):
He saw it thirty/a hundred/many/innumerable/a great number of times.
When the quantifying adjective is an ordinal number (or last), however, the prepositional construction with for is used, although again, for may be omitted:
He saw it (for) the first/second/last time today.
Thus confusion between for the thirtieth time and thirty times may have helped to lead the author of (1) astray. A further source of confusion regarding (1) may be the adverbial use of long as equivalent to for a long time in non-assertive (i.e. negative and interrogative) sentences such as
Did he stay long?
He didn't stay long.
This usage also occurs in assertive contexts with certain verbs of belief, assumption, attitude, and speaking–especially in combination with certain other adverbs (e.g. long and hard, long and carefully, etc.). For example:
Film has long been considered an art form.
I've thought long and hard about this problem.
I've long admired his ability to handle people.
This event will be long discussed.
Note that think in (1) does not mean 'have the opinion,' and thus is not a verb of belief, assumption or attitude; it refers to the mental activity of thinking, i.e. 'meditate, cogitate.'
otherwhere vs. elsewhere
According to the Oxford English Dictionary, otherwhere (meaning 'elsewhere') became obsolete in the 18th Century, though subsequently was revived and can be found in l9th Century literature. Nevertheless, it is certainly obsolete as far as present-day standard English is concerned. The same is true of all combinations with other, except otherwise (also the adjective otherworldly), which may have been current in English at one time, or perhaps still are in some dialects–i.e. otherwards. otherwhat, otherwhile, otherwhence, otherwhither. The German learner, of course, is much more likely to be translating anderswo than to be dredging up 19th Century words.