Where are the declension numbers?
So, I tried out Russian, and it looks good except that when you scroll over a noun, it doesn't have either gender or more importantly declension number. How will I know which set of endings go with a noun?
The nominative singular ending of a noun usually determines its declension. There are basically three declensions in Russian: one for masculine nouns, one for feminine and one neuter. I'm sure that in the "tips & notes" of at least one of the lessons they explain what endings determine what declension / gender.
Edit: It's not anything like Latin, where they have 5 declensions where a masculine noun can belong to one of three of those declensions. In Russian, once you learn the gender of a noun, you can determine which declension to use. Therefore, declension number isn't necessary.
I've already seen someone confused that masculine "папа" is declined as feminine "мама", so let's get it straight.
On the contrary, Russian/Slav declensions are closer to Latin being inherited from one root. For instance, "agricola" (masculine) and "silva" (feminine) are of the 1st declension and declined similarly, same goes for Russian "папа" and "мама", and "сирота" (common gender). Ночь (3d decl.) and страна (1st decl.) are both feminine but different declensions thus declined differently. That's why all Russian children learn declensions in their schools.
Of course, Russian declensions are way simpler than Latin nowadays, but the ancient remnants are all around as irregularities: в меду+в мёде (but only во льду), из дому+из дома, мать/матери (lat. mater), семя/семени (lat. eng. semen), путь/пути (masculine) and so on, if you see that something is declined irregularly then you may be sure that it is a remnant of the ancient declensions (5-6) system and reduced words.
I am not sure I would go as far as giving a user a NUMBER specifying the declension patters. The reason is, two systems are used. Some scientific classifications call the declension of a noun like мальчик and окно 1st declension and the pattern for мама 2nd declension. In Russian schools, however, the declension of мама is "1st declension". So the meaning of the number depends on who you ask.
I think additional information about the words should be provided. I hope Duolingo implements that feature for incubated courses sooner rather than later.