I don't see anything wrong with the text itself, is the file named properly? If that is for oak leaves, the mcmeta file should be named leaves_oak.png.mcmeta (notice the full file name is in the mcmeta name, including the png extension just before the .mcmeta extension). If the option is available, make sure you're saving as UTF-8 without BOM.
If those aren't the issue, please set the launcher to stay open, and then look in the game output and find the errors with leaves and that should tell you what the issue is.
Alright, thanks so much! I haven't tested it just yet, but my version was oak_leaves.mcmeta so I'll take a look and give you an edit in a minute!
EDIT: Alright, tested it and it works great! There is one problem... The birch and spruce leaves are still green, being overlayed in the code. Could someone tell me what I need to do with the leaf textures in order to counteract that?
EDIT 2.0: My picture size is 64x256, but there is a line of weird, different color on the ends of all the leaf textures. Could someone tell me how to redo the textures in order for it to fit the block correctly?