HOW CAN I TELL IF ´YOU´ IS PLURAL OR SINGULAR
You cannot. However, if you make sure that you use DU and DIN, or I and JERES, then the program will accept either, but you must commit to singular or plural and not try to mix them.
Am I correct when I say it is either I and jeres or Du and din?
Yes except that you don't capitalize "du" (with "I" always being capitalized).
Can't "I fortæller mig om din edderkop" also work? I thought I could use either "I" or "du" for "you"
Well, depends om context. I = you is plural, du = you is singular. But om this case, both is right - unless you are in a course for singular sentences
Yeah shouldn't both be right here??
Just a thought, but you could easily drop a cue in parentheses letting folks know you are looking for the plural versus singular translation. Just put (plural form) in front of the sentence.
I used Du instead of I for the first word (everything else was EXACTLY the same) and it didn't give it to me. Why?
"Du fortæller mig om din edderkop" is also accepted.
I thought it wasn't, but I tested it out and my mistake was in an ending of edderkop :D
it does not accept the singular
Why is "edderkoppen din" not accepted ?
Because in Danish we add the possessive pronoun before the thing that is owned. "Edderkoppen din" sounds Norwegian to me.