Generally, the Russian scientific research degree "doctor nauk" is granted for investigating unresolvable and more universal scientfic topics and not for new and uninvestigated and particular scientfic problems as it is in tne case of PhD degree attainment. Therefore, PhD degree, frome these respective, more corresponds with Candidate of sciences degree. But PhD dissertation in social sciences usually is much bigger in length. If PhD dissertation consists of at least 80 000 words, the Candidate of sciences dissertation consists of nearly from 40 000 to 60 000 words. But the tasks of the dissertations and necessary demands of the individual contribution in the particular science are the same.This contribution sounds like "the scientifical novelty", which is necessary declared in the Russian and other CIS countries' candidate of sciences dissertations' introductions. The Bologna system is not applied to the post-graduate degrees, so candidate of sciences oficially and "doctor nauk" degrees are called "scientific degrees" and they are not called "academic" degrees. For the "doctor nauk" degree attainment there are needed the new resolution method for the problems which cannot be resolved by old methods.
The most correct translation in my opinion are next:
- PhD - доктор философии из (name of science(s) in respective grammar case.
2)PhD student - учащийся (учащаяся) (or студент(студентка) в учреждении (учреждения),or департаменте (департамента) etc. на соискание ученой степени Доктора философии (из) (...) при or в (name of university, country etc., or соискатель ученой степени Доктора философии из... при or в (name of the university, etc.)
In the RuassianRussian official procedures there the copy of PhD holder certification is needed, probably, as well as there are need of any document affirming status of PhD student for the personal status clarification. Analoguous translations are useful for M.D. and other equivalents of PhD. In the case of the DSc there is also useful to clarify the content of the degree meaning (as it is in the case of informal communication) by adding an explanation concerning a country which academical degree was attained in (e.g. Я доктор философских наук, германская ученая степень).