Selling from the UK into Germany is geographically easy and institutionally not. Speaking the same language does not mean being under the same rules, and the gap shows up most on invoicing and data.
Most German corporate buyers can work in English, which makes the sale easier and misleads on the product side. On contracts, invoices, imprint and support the German expectation remains. The most common mistake we see is a sales conversation that runs smoothly in English and then arrives at a product that is not ready in German.
If you ship physical products, customs, VAT and delivery terms become a project of their own, and that is usually a logistics and tax question rather than a software one. If you sell software or services, the real subject is invoicing and data. What both share is that the systems have to know which regime they are operating under.
Data moving between the EU and the UK requires a separate basis on the contractual side, and which basis fits your case is a legal question that goes to partner law firms. The consequence on our side is this: which data crosses the border must be visible from the start, and where possible the architecture should not require the transfer at all.
For some activities yes, for others no, and it depends on what you do; we settle that with a partner law firm. What matters from our side is that whatever the answer, the invoice can be produced under the correct legal entity and with the correct fields.
For enterprise software often not, though it makes a difference; selling to consumers it effectively is required. The middle path is to leave the interface in English while building invoicing, imprint, privacy notice and support in German. That combination produces the most visible difference for the least cost.
Tell us what you sell and where the customer sits. We will say which side has to be solved first.