No: a representative can sign for you, but the land registry (Grundbuchamt) recognises the representative's authority only if the signature on the power of attorney is notarially certified (§ 29 GBO). Abroad, this is done by a German consulate or by a local notary whose certificate is then apostilled or legalised. If you attend yourself without sufficient German, the notary translates the contract instead of reading it to you — personally or through an interpreter (§ 16 BeurkG).
What to check:
• the power of attorney is drafted by a German notary for the specific transaction and covers the contract, the conveyance and, if a loan is needed, the land charge;
• the signature is certified at a German consulate or by a local notary — with an apostille or legalisation and a certified translation;
• the original power of attorney reaches the German notary before the day of signing;
• if you attend yourself, the interpreter is agreed in advance and a written translation ordered;
• for a buying company, proof of its representatives' authority and its entry in the Transparency Register (Transparenzregister) are ready.