In the Russian language, the most interesting case is the letter “Г” (like G in 'go'), which may represent five different sounds. Here they are:
1. [g] when it comes before the vowels а, о, у, э, i.e. letters that does not imply palatalization of the preceding consonant. Also when comes before voiced consonants. Examples: гол [gol] (goal in a football or hockey), гул [gool] (hum), гром [grom] (thunder).
2. [g'], soft g, when it comes before letters that imply palatalization of the preceding consonant, like и or е. Examples: ген [gen] (gene), гимн [gimn] (anthem).
3. [k] when the last letter in a word or when comes before unvoiced consonant. Example: рог [rok] (horn), ЗАГС [zaks] (registry office in Russia)
4. [v] in the endings of adjectives and pronouns in Genitive. Example: его [yivò] (him/his), злого [zlòva] (of smb. angry)
5. [ɦ] in some idioms/ interjections. Examples: Прости Господи [prasti ɦòspadi] (Lord have mercy, lit. Lord forgive me), ради Бога [radi bòɦa] (for God's sake).
While the first three sounds comes from the very nature of the Russian phonetic system (the regular opposition of hard and soft sounds and the rule of un-voicing the voiced consonants in the end of words), the latter two sounds are nothing else but tradition. The г ->в change is irregular and works only for adjectives and pronouns. In Russia's South and Ukraine, [ɦ] is common, so in the idioms, which mostly refer to the God, it's the influence of the Southern dialect, however, besides the idioms, Russians normally pronounce [g] in the words mentioned above.
The good news is that other Russian letters are more predictable and represent less sounds than Г. Happy language learning!
The Russian letter Г/G drawn by Ankita. All the things in the picture start with Г: Глаз (an eye), Галстук (a tie), Галоша (a rubber shoe), Гвоздь (a nail).