You find more details to start with OXID eShop under Getting Started for User, Seller and Developer
Unfortunately, OXID eSales has partially switched off the Forge content. You can find more information about language management at Language handling • OXIDforge or Understanding the OXID eShop template hierarchy and override system — OXID eShop developer documentation 6.5.0 documentation
If you need professional help, you can find contacts at OXID Forge – The knowledge base of the OXID eShop