How do you say "there aren't people I can talk to" ? 没有对他们可以说话的人？or else "the person with whom I had a fight last week is now a friend" and all those sentences that require with/to/etc.?
"There aren't people I can talk to"
The translation varies, depending on what word is used to translate "talk to".
With "倾诉对象", the sentence is starting to become idiomatic. Other variants are also possible. For example, you can replace "找不到" with "没有". If the context permits, you can also say "没有人可以／愿意倾听／聆听我的倾诉". This last sentence is closer to "Nobody could/would become my listener".
The key here is that you need to find a word that conveys the meaning of "talk to" instead of just "talk". In other words, it should emphasize the action on the subject's part. Otherwise the sentence will just become awkward because you need to make up for the missed meaning. This is why dictionary translations of "talk" like "交谈" and "谈话" will get you nowhere---these words can only mean "talk with", which give equal weights to both parties involved in talking. Structurally this is similar to the deletion of preposition mentioned by Joe. But I think that this is more absorbing the meaning of the preposition into the verb than implying that meaning through the verb.
"The person with whom I had a fight last week is now a friend"
I find this translation better than any attempt to simplistically duplicate the sentence structure:
The key here is that unlike in the original sentence, "the person" is now the implicit subject of the relative clause. This technique works trivially when the clause describes a reciprocal action with "with". Sometimes, even if the action is not reciprocal, you can also get it to work by replacing the verb of the clause with its antonym. For example, for
you can say
Comparing with a sentence using the "dummy variable" approach mentioned by Joe,
the former just sounds much more natural and less twisted.
How about "all those sentences that require with/to/etc."?
The two examples above show that you need to adapt the expression to the meaning of the preposition of the clause. But the way of adapting is different in the two examples. I doubt that general rules exist for all such sentences even though I am no linguist. But perhaps there exists this one technique that in many, even if not all, cases can at least make you sound less awkward and more comprehensible with little effort---use more than one sentence. For example, again consider the "sold my bike" example above. You can use these two sentences:
which are totally fine and even easier to understand than "我卖了自行车给他的那个人……". This sacrifices on structural "信" in order to gain on semantic "达" and "雅" of Yan Fu's principles of translation. Sometimes, especially for complex sentences, this is probably the only sensible solution.
I think the first sentence in Chinese can be said
and the second one can be said
(Adapted from Linguistics answer I gave)
Translating sentences like these can be problematic because you can't leave dangling prepositions. It used to really bother me because it wasn't hit on by grammar books, it's hard to google, and it can be difficult to convey to a person that "I want a general strategy for translating these kinds of sentences" and are not merely asking for a translation of a particular sentence. Here are some example sentences I've found along with various ways of fixing the ungrammaticality of the obvious translations:
It seems there are a few different grammatical strategies:
Looking at Timothy's answer, his first sentence changes the verb and then deletes the preposition. The second uses the "dummy variable" approach.
Notes on glosses:
CL = Classifier, as in the measure words in Chinese (e.g., 个).
REL = Relativizer; the 的 particle which links adjectives or relative clauses to nouns.
PFV = Perfective; the 了 particle which marks for completedness of verbs.