Do not worry, Wifi pass phrases for personal use should only be in printable ASCII characters , in other words English characters.
They do not support Unicode or other codepages.
For more details check the Wikipedia's Wi-Fi Protected Access page .
Except if you are redirected to a webpage for authentication, that's a whole different story and Karlson's answer is applicable.
travel.stackexchange.com/users/10051/Nean Der Thal
For Android depending on the model of your phone you may have to add Russian Language to the available keyboards.
I have Galaxy S5 and under Settings -> Languages and Input
you should be able to do this from the Galaxy App Store.
You should be able to do the same for the iPad just add a Russian Language, which will allow you to switch to it and make the keyboard available for use.
travel.stackexchange.com/users/1372/Karlson
I am Russian and I never met a WiFi password in Cyrillic.
travel.stackexchange.com/users/36089/enf644
I traveled in Russia in 2011 with a tablet, smartphone, Vita etc.
Every WiFi network was in Latin characters.
As with most nations they try to be somewhat accommodating to tourists and English is a good baseline, even for people on holiday from other parts of Europe.
travel.stackexchange.com/users/36064/Preston Crawford
I've been living in Russia for 3 years, lived in various hostels and hotels, but I never saw a Wi-Fi with a cyrillic password anywhere.
I'm not even sure that it's technically possible.
travel.stackexchange.com/users/32525/Mentiflectax
I have been to Russia.
Once I was hosted by a friend in Moscow.
He said I could use the wifi.
He gave me the password.
Accessing to his wifi was just like anywhere else on the planet.
Here i show you a ticket of a Cafetería in Moscow called Costa Coffee where they specify the login and password to access their wifi.
As you can see, it is in latin alphabet.
Take a look .
travel.stackexchange.com/users/13381/Pathros
I'm about to travel to Russia, and I made sure to book only accommodations that offer Wi-Fi to its customers, but a question came to my mind.  As Cyrillic is the standard alphabet in Russia, is there a chance that the passwords in Wi-Fi networks will have to be entered in this alphabet? How do I know which keys to press on a Latin keyboard, so that my devices can connect to the network?
Will Wi-Fi passwords in Russia be in Cyrillic? How do I type them on a Latin keyboard?
travel.stackexchange.com
<russia><tips-and-tricks><electronic-items><wifi>
travel.stackexchange.com/questions/57178
travel.stackexchange.com/users/24596/gmauch
You may have to add Russian language to the available keyboards, but Wifi pass phrases  for personal use  should only be in printable ASCII characters and you shouldn't need it for this purpose. Russian WiFi passowrds use English letters, however, Android phone users can add the Cyrillic keyboard if they wish.
WiFi passwords in Russia use the English alphabet. A russian keyboard can be added to your Android phone if you wish.