I have long been perplexed by the inconsistencies of my mother tongue, French. This feeling has only been exacerbated by learning more languages, and spending a long time outside French-speaking countries.
French is first of all a very irregular language. Why is it that normal plural take "-s" at the end, but some words take "-x" ? Why is it for instance that the plural of "cheval" (horse) is "chevaux", but the plural of "festival" is "festivals" ? A rule says that words ending in -au or -eu take "x", but with so many exceptions that it is hardly a rule anymore. E.g. we say "des yeux bleus" (blue eyes) and not "des yeux bleux". As we are at it, why does the plural of "oeil" (eye) become "yeux" ? It doesn't sound or look any similar !
Irregularities abound in French, as much in spelling as in grammar. We write "oignon" but say "onion". English has taken this word from French in the Middle Ages, so I suppose the most usual spelling at the time was "onion", which fits perfectly the modern French pronuciation. So why did those stuck up Academiciens decide that the proper spelling had to be an antiquated "oignon" that does not fit modern pronuciation, while French is on the whole fairly regular when it comes to pronuciation ? (one vowel or group of vowels almost always has the same pronuciation, contrarily to English).
But French is not just the most irregular language I know, it is also the most illogical. This is paradoxal as French people tend to be quite logical and rational people ("cartesien" as they say), and the structure of French language make it easy to express ideas logically.
Let me illustrate this. "Sans doute" literally means "without doubt". So one could imagine it means "for sure" or "certainly". But it doesn't. Its meaning is more like "perhaps" or "maybe". So why say "without doubt" if you mean "peut-etre" (maybe) ?
It is a very common tendency in French to change the meaning of French expressions (not even those of foreign words, as is usual in Japanese !).
Some expressions are not really illogical, but for the least far fetched. "Rien a voir", literally means "nothing to see", but does not mean there is nothing to see. It means that it is "unrelated".
These are not even metaphorical idioms. They abound in French like in English. For example, "prendre ses james a son coup" (lit. "to take one's legs to one's neck") means "to hurry". I have no problem with that. It's just an image - although some idioms have such an obscure origin that many native speakers even wonder what it means when they hear it. Some are so common that only learners of French may have problems with them (e.g. "ca me fait une belle jambe" literaly translates as "that makes me a nice leg", but means "it doesn't help" or "I don't care").
Why is it that "bon sang !" (lit. "good blood") means "damm it !" ? Where does that come from ? A more colloquial version is "bon sang de bonsoir !", which is even worse : "good blood of good evening !"
Worst of all, French is not really flexible (especially compared to English). There are some aberrations that I just can't accept. Why is it that there is no word for "cheap", or that the word "inconvenient" exist in French (same spelling, different pronuciation), but not "convenient" or even "inconvenience" ? The irony is that those English words came from Old French, but have disappeared in modern French ! There is not even a word for "convenience store" in French (except in Quebecois). How inconvenient in daily speech.
There are many other examples of "missing words" in modern French. E.g. "ubiquitous", "conspicuous", "ravenous" and "promiscuous" all come from Latin or Old French, but have all disappeared from modern French. Why "kill off" useful daily words like that ? No wonder French ended up having 7x less words than English in total.
After living in Japan, everytime I went back to Belgium or France, or watched French movies in Japan, I noticed that French was just full of such senseless (or at least weird or illogical) expressions. The list would be too exhaustive to put here. I never questioned these expressions before. But as my mind is more tuned to English or Japanese now, I can't help but notice how corrupted a language modern French is. In comparison, the meaning of words in English seem so logical and straightforward (apart from idiomatic expressions and varying pronuciation).
Do you have similar comments to make about your language (other than English) ?