Kenneth Katzner has set himself a difficult task--review the languages of the world in a reasonably-sized volume. This means that, inevitably, a lot of important detail is going to be left out. Most, but not all, nations have their national languages recognized here. Some smaller languages are included both for completeness and for examples of interesting linguistic variations. One, Naxi, spoken in Yunnan, China, is still written with little pictures; a stick figure jumping represents dancing, for instance.
Some other reviewers have complained that there is a lack of detail about the writing systems, so that seeing the original language and its translation is not that helpful. This does not account for the complexity of some of these alphabets, like Burmese or Thai or Devenagari (Hindi and some other Indian languages); which have a LOT of letters and modifications of letters. Once you start down that road, the book could easily double in size! However, he does explain a little about how some alphabets work, like how Korean (Hangul alphabet) has its letters grouped into little three-letter clusters, not written in a straight line.
One major improvement that would help a future edition of the book: Typeset the foreign languages! Clearly, some samples are photoreproduced from old sources, and the letters are unclear and hard to see and/or of poor overall quality (and vary in size from language to language, even languages using the same alphabet). This is particularly noticeable with some of the odder Asian scripts. The Unicode project is trying to allow computers to recognize nearly any script (even obscure ones); the next edition of this book should take advantage of such advances and typeset those languages that are not in this edition.
Another useful item, but harder to implement, would be detailed transliterations of each foreign language passage (at least those in non-Roman scripts). Then the reader could see (at least approximately) how various words and letters are written and spoken in the language in question. This opens up a whole new set of problems, of course; Mandarin Chinese and Cantonese are the same in writing but vastly different in speech, so would they both have to be represented? That dialect question would crop up a lot. Some languages are written in more than one script, too, or have transitioned from one to another recently. Showing such languages in both scripts is fun, but rarely done in this book, even when the book mentions that the language has multiple scripts.
But overall, the book is a fun introduction to many languages and will familiarize the reader with the "look" of many of them.