Is it true that in Japan a citizen's name has to be in kanji, and not in hiragana?

Katakana is a phonetic script (so is hiragana) and it does not have a meaning by itself (like kanji). There are some English sounds that don't exist in Japanese. (L, V, W etc.) Therefore when foreign names are translated into katakana, the pronunciation might be changed a little bit. katakana is normally used to write foreign names, Kanji is generally not used to write foreign names. . although foreign names can be translated into kanji, they are translated purely on a phonetic basis and in most cases will have no recognizable meaning. Kanji are ideograms, i.e. each character has its own meaning and corresponds to a word. By combining characters, more words can be created. For example, the combination of "electricity" with "car" means "train". There are several ten thousands of characters, of which 2000 to 3000 are required to understand newspapers. Before the introduction of Chinese characters, no Japanese writing system existed. When adopting the characters, the Japanese did not only introduce the characters' original Chinese pronunciations, but also associated them with the corresponding, native Japanese words and their pronunciations. Consequently, most kanji can still be pronounced in at least two ways, a Chinese (on yomi) and a Japanese (kun yomi) way, which considerably further complicates the study of the Japanese language. Kanji are used for writing nouns, adjectives, adverbs and verbs. But unlike the Chinese language, Japanese cannot be written entirely in kanji. For grammatical endings and words without corresponding kanji, two additional, syllable based scripts are being used, hiragana and katakana, each consisting of 46 syllables.

No. According to the following site you're required to adopt a Japanese family name when applying for citizenship but this rule has been relaxed lately and some people have been allowed to register their own (non-Japanese) name written in katakana. So apparently kanji isn't a requirement. There are restrictions on which kanji can be used for both first names and family names.

It's common for first names to be registered in hiragana. Friends of mine had wanted to use a particular kanji for their daughter's name but it wasn't on the list of allowed names - so they initially registered her name in hiragana. When the list was updated some years later and that kanji became available they officially changed her name to the kanji.

https://en.wikipedia.org/wiki/Koseki

So how are Japanese telephone books organised? Do all the kanji characters have some particular order?

Phone books are organised phonetically regardless of the kanji characters used - in the same order as hiragana/katakana are usually written (a-i-u-e-o-ka-ki-ku-ke-ko...and so forth). The same is true of dictionaries.

The other way in which kanji can be organised is by the number of strokes used to write them - which is the case, for example, with reference books for people learning Japanese as a foreign language.

Can I get a definite answer on the fact that *L* sounds don't exist in Japanese? I've observed some cases in which a name spelled (in English translations) with an *r* are pronounced with *L* sounds. The common explanation I've received for this frustration is "R sounds like L in Japanese". Can someone explain it better?