Na'vi is the constructed language of the inhabitants of the moon Pandora in the fiction movie Avatar. Though its native speakers have no writing system (as far as we know), Na'vi is represented in Latin script for earthlings' learning purposes.
The alphabet is the same as English, except for the accented vowels ì and ä, plus a glottal stop represented by ’ . All of the required characters can be made easily using the normal US keyboard layout -- ì is Option/alt + ` then i, and ä is Option/alt + u, then a.
While the author of the language has employed underlines to indicate syllable stress, this is impossible in plain text, so an acute accent might be used as an alternative (made via Option/alt + e, then the vowel).
Ideally for digital representation of Na'vi something other than the straight or curly Apostrophe (U+0027 or U+2019) should be used for the glottal stop, because this character is actually "punctuation" rather than a "letter" and is often ignored in text processing operations like sorting, matching, and searching. Also it cannot be used in an internet domain name.
To avoid such problems one can use the Modifier Letter Turned Comma (U+02BB) or the Modifier Letter Apostrophe (U+02BC). The former is found for the glottal stop in Hawaiian (called ʻOkina) and the latter in Navajo. Unfortunately these are not available on the US keyboard, so one would have to make a custom layout for Naʻvi.
You can download an experimental Na'vi keyboard here. It puts ì, ä, and U+02BC on the [, ], and \ keys, and the acute accent vowels on the Option/alt keys.
For a good site with materials and forums on Na'vi, see Learnnavi.org.
For the language creator's site, see http://naviteri.org/