nothing
each unown has its own letter. it is hard to read but you can make out some words. it is in English, so it is not a foreign language
shier piller
They will just be patience. Walk around any room in the ruins espespecialy in the rooms with just a rock, walk constantly around it until you meet an unknown. Each unknown are different in each room to.
18, one for each type
There is no such thing, BUT.. you can do each Pokemon one-by-one
neither of them is better, they are both the same, but in diamond, you catch dialga, and in pearl, you catch palkia, and you can catch different Pokemon in each game for example: you can catch this Pokemon in diamond, but not pearl but: you can catch this different Pokemon in pearl, but not diamond
One each.
Do you mean trade from Diamond to Platinum?? If so, you need two ds's and a copy of each, sorry bad answer.
fire stone evee
You can get it by talking to Dawn/ Lucas's sister in Pearl or Diamond. Each day they tell you a different species of Pokemon is swarming, and where to find it. The Pokemon changes each day, so Cubone will eventually be swarming, if it isn't today.
based on luck, while catching Pokemon check each time for that nature
Each Pokemon diamond game has a different ID. You can find the ID by looking at the numbers in the lower left corner of your game cartridge.