With Wordalist, you can practice writing in just about any language. But to be able to write in any language, you need to add the necessary keyboard layout to your device. So, to be able to practice Russian, you need to add the cyrillic alphabet to your device.
Adding one or several keyboard layouts to a Mac running OS X is easy:
Do you have a latin keyboard? When adding non-latin keyboards, look for phonetic layouts. For example, Russian is available both as the standard layout, but also with a phonetic alternative, which maps equivalent letters onto your current keyboard. This makes it a whole lot easier to write in Russian as the latin labels on your keyboard match the closest cyrillic letters.
Here's a guide from Apple: https://support.apple.com/kb/PH18448?locale=en_US
Adding a new keyboard layout to an iPhone or iPad is just as easy:
Now, iOS will show a globe-icon in your keyboard. By clicking this icon, you quickly switch between your available keyboards.
Read more about the different settings here: https://support.apple.com/en-mo/HT202178
So, not being a Windows-user myself, this one doesn't come naturally to me. But here are instructions for two of the latest Windows versions:
This can be a bit different between different Android phones, as manufacturers can choose to customize their version of the operating system. But for most phones, these instructions should do:
Here are some more detailed instructions: http://www.beginandroid.com/keyboard.shtml