I still have trouble understanding how I'm supposed to reduce vowels in long words. Because in some words like cвидания, the unstressed "я" becomes /jə/; while in others like язык, it sounds more like /jɪ/.
Same happens with "e", or at least that's what it seems to me. I feel the ones in "телефон" sound more markedly like /jɪ/ than the one in "очень", for example.
Could it be I'm just wrong? If so, can anybody point out to me what the right pronunciation is for these vowels?
First of all, "я" = "ja" (or "softsign+a") and it's "a" that we reduce.
The actual reduction of vowels may change from word to word and from speaker to speaker. Much like English-speakers have a dozen different pronunciations for "e". You may even not reduce vowels at all, though it's quite an unusual way of talking. That is both "jezyk" and "jizyk" are OK, while "jazyk" sounds like you've just come from some tiny village in the Siberian wilderness where the people are as slow as the seasons of the year ;-)
But never ever confuse ja/je/ji with its "simply-soft"-counterpart. That is "t'el'ifon" or "t'il'ifon" are both OK, yet "t'eljifon" is just an epic fail.
Whether an unstressed back vowel o or a, these phonemes reduce identically. If it is in word-initial or pre-tonic (immediately before the stressed syllable) position it will be [ʌ], somewhere between a Russian schwa and an [a]. In all other places, unstressed o and a will be the Russian schwa [ə] (which is closer to [a] than English schwa.
Exceptions include when я is written "a" because of a spelling rule, but follows a soft consonant such as ч or щ. In this case the unstressed vowel will reduce as below. Also, if the я is both unstressed and the word-final phoneme, it further reduces to [ə].
With the vowels е, и, and я the unstressed phoneme becomes [ɪ] in most cases. Exceptions include when e or и are written only because of spelling rules, but in reality are [э] and [ы], and will reduce to [ɪ] (цеплять, шить, жираф.)
In standard Russian pronunciation based on the Moscow dialect, я or a consonant ending in -я, or one of the soft syllables ча or ща have the vowel reduced to [ɪ] when they occur directly before the stressed syllable.
ча or ща theoretically represent the sound combinations чя and щя, yet since ч and щ are considered inherently soft consonants by their own right, the spelling with -a- is orthographically correct and logical in order to avoid a "double softness" in the spelling.
Note the following:
язы́к [jɪˈzɨk] яйцо́ [jɪjˈʦo] я́йца [ˈjajʦɐ] яи́ц [jɪˈiʦ]
час [tʃas] but часо́в [tʃɪˈsof]
я́сно [ˈjasnɐ] but объясни́ [ɐbjɪsˈɲi]
When in doubt, you can go to this site and enter any word or word form, and it will indicate the pronunciation with all the correct vowel reductions using the cyrillic phonetic transcription, which is easy enough to understand. Just be sure to choose словоформы in the dropdown next to the search field. Otherwise, you'll just get a list of words that rhyme with your entry.
Strangely, in English there is a similar thing whereby "telephone" can be pronounced "tel-ee-phone" to affect an accent. It's interesting that the Russian version is quite similar in its pronunciation. I have no doubt it is an internationalism and was influenced accordingly.
