I don't really understand the question either...
Konstantin, you're referring to the Conditional with your German example.
Indirect speech in German works differently as the Conjunctive has to be used in formal German, which however, can be replaced by the Conditional (would+infinitive).
In English, the tenses have to be shiftes back from direct to indirect speech - .... but NOW - that I've been thinking about this, I might have got an idea of what maj's question aimed at:
The modals "can" and "may" only occur in their forms in simple present and simple past tense, "must" is used in simple present tense only. Now, if you have a sentence including one of these modals, that need to be shifted back, you've to use substitute forms for all of these three modal helping verbs:
Linda: "He can speak English" -------- Linda said he "was able to" (could) speak English.
Linda: "He could speak English" ------ Linda said he "had been able to" speak English.
Linda: "He may go" -------------------- Linda said he "was allowed to" (might) go.
Linda: "He might go" ------------------ Linda said he "had been allowed to" go.
Linda: "He must leave" ----------------- Linda said he "had to" leave.
Linda: "He had to leave" --------------- Linda said he "had had to" leave.
("might" and "could" are commonly usually used as conjunctive forms though, but can express past tense also)
As you can see in these examples, some modals cannot appear in their own forms in special indirect sentences, so maybe that was the problem, maj was aiming at?!
Hope I could help...