VDE-AR-N 4105, officially titled "Generators connected to the low-voltage distribution network – Technical requirements for the connection to and parallel operation with low-voltage distribution networks," is the binding technical standard issued by the VDE (Association for Electrical, Electronic & Information Technologies) under the authority of the German Forum for Network Technology (FNN).
While the full standard is proprietary, official English translations and related guides are available: vde-ar-n 4105 english pdf
Your English PDF will contain tables of emission limits. The inverter must not inject excessive harmonics (3rd, 5th, 7th, etc.) into the grid. Compliance with EN 61000-3-2 and EN 61000-3-12 is referenced. vde-ar-n 4105 english pdf