Well, for "die Regen". It could be taken for the river, although that one takes the "der". It's also simply the plural of Regen. "Die Regen der letzten Woche haben wieder einmal gezeigt, dass..."
I'd not consider English to be very flexible. Word order is actually very important in English.
"The cat ate the fish." gets a totally different meaning when the words get switched to "The fish ate the cat." With the cases in German that doesn't happen. "Die Katze frass den Fisch." has the same meaning as "Den Fisch frass die Katze.", just the emphasis gets shifted. One could even do "Den Fisch die Katze frass." or "Die Katze den Fisch frass."
In my experience the "false friends" are really difficult for Germans. We really got to learn that "freedom" isn't "Frieden" (peace). That "who" is "wer" and "where" is "wo". And that you "get" (bekommen) a car, not become one. And the aforementioned word order which is much more strict in English.
As for Japanese, it may not have so many tenses, but it has lots of it's own declinations, conjugations and other traps, depending upon politeness, tense, negative/positive, etc, etc. One easily gets more versions for a verb than one gets with the English tenses.
Or take "I", in Japanese depending upon who you are and whom you are speaking to you'd use "watashi", "ore", "boku", "atashi" or one of several more possibilities.
