So... my resource pack don't work correctly, i mean i changed the sounds, the textures of the polar bear, the llamas and the glowstone block. The Polar Bear is working, and the sounds as well but the Llamas and the Glowstone are not working. Also my resource pack says in the resource pack menu the following text: "Made for an older version" so i launched the Minecraft in 1.14, 1.14.2, 1.14.3, 1.14.4 (latest) instead of 1.14.1 but nothing, in my assets folder there are mobs like fox, panda and so on so i don't think i should try out in 1.13 (also my brother's 1.7.10 resource pack works in 1.14 with the 1.7.10 blocks and sounds so idk)
The Meaning of Life, the Universe, and Everything.
The 'Made for an older version of minecraft' warning comes from the pack.mcmeta file. If you look inside it you should see a "pack format" line and for 1.13 and 1.14 you want the format to be 4, they change the format number any time they do a large overhaul of textures. In 1.13 the folder names were changed for 'items' and 'blocks' to 'item' and 'block' so you'll want to make sure you delete the s at the end of the folder names there if you want to see your items and blocks in the world properly. You also said 'in my assets folder there are mobs like fox, panda and so on' which I hope is incorrect and that you have you llama texture inside a folder at assets/minecraft/textures/entity/llama and your panda in a folder at assets/minecraft/textures/entity/bear- sound like you have the bear in the right place at least. It would be easier to see what's wrong if you could uploaded a minimum pack of what you've done so far but I'll guess at what I can.
If your brother's 1.7 pack works at all for blocks and items in 1.14 it would almost certainly be because of optifine features or altered block models telling the game to look inside the 'blocks' folder even though it doesn't exist in the game. There should be very little compatibility between a pack made in 1.12 or earlier and a pack made for 1.14 since 1.13 and 1.14 changed a lot of names and file structures so they don't work the way they did before.