Slovenian railways have special fares for those under 26 (30% lower than standard fares), but they seem to require some card as proof of eligibility. Slovenian railways' website mentions "SŽ discount card" while wikitravel refers to "Euro26 youth card". How do I (20 yo, student in Moscow) get this discount?
I agree that the information on the linked webpage is useless. The
SŽ discount card refers to
SŽ-Ej!KArtica card (webpage in Slovenian), which is a localized co-branded variant of the European Youth Card. There is also a localised non-branded version, called
Ej!Kartica, which does not provide the same benefits (no rail related discounts) and is therefore equal to the youth cards purchased in other countries.
It seems (terms and conditions in Slovenian) that this version is available only to permanent and temporary residents, aged 12-26, that pay the yearly subscription fee (10€ at the time of writing), which might exclude you. The absence of translations of this webpage seems to confirm the suspicion that it is only intended for locals. Note that the discount only seems possible with this specific co-branded card, not the youth cards that may be purchased in other countries. Searching the international discount database does find the Slovenian railways, but there's a remark, claiming that
SŽ-Ej!KArtica is needed.
The reason for residence requirement appears to be that these cards are mailed-only, meaning you need a local address to mail to. It might be worth to ask the railroad company about this directly, to see if this can be wroked around. You can find the email at the bottom of the page which you linked (the potnik.info one). Just send them an email in English.