"Det finns många länder."

Translation: There are many countries.

[magdalena.butra]

Previously, I had just 'land" and I could translated as "land" or "country". Now, when there is plural, duolingo accepts only "countries", no "lands". Why?

[gramphos]

There are several meanings of land. The one that means nation, state or country has the plural form länder.

The other meanings have unchanged plural.

• land could mean land as in "land ahoy" (land ohoy)
• land could mean (garden) plot
• landet could also mean the countryside (that form wouldn't be used in indefinite form unless as part of a compound word.)

[jstnc]

Is there a reason the a turns to ä in the plural form or is it just something you have to remember?

[Yuki_Shiro]

It is to remember I think, but it does not seem uncommon.

Man männen, for example

[Arnauti]

There aren't that many of them: here's a link to a list: https://www.duolingo.com/comment/5886811