"fordern" conveys a meaning of demand that is not present in the other translations in English and French...

The Japanese uses the command form ～なさい, so it is a good match for the only sentence it is directly linked to.

then the French, English and Spanish translations must be wrong...

Well I don't understand the Japanese sentence, but the German sentence is not correct:
"Er forderte uns auf, sofort anzufangen." would be a correct German sentence (I don't know if it would be a correct translation).

it would still not match the French, English and Spanish and probably Portugese...

That would be no Problem for the German sentence, as the system of Tatoeba is that a sentence has only to match its DIRECT translations. So the only question here is if it matches the Japanese translation.

I understand, but b_p confirmed there is in Japanese a meaning of "command" that is not conveyed in these languages when it is in German, confirming these translations are wrong...

Actually I think "told us to ..." is much more of a reported command than a reported request (e.g. "asked us to ..."). So I think the English is a good match to the Japanese.

I'm not good at English at all, but I suppose English sentence needs "...", and also Japanese needs 「... 」.

ちょっと分かりません。英文は「told us to start at once」で、日本文は「すぐに出発しなさい、と言った」なので、・・・をどこに入れていいですか。

まず、この日本文には「」があるべきだと思います。つまり：
彼は私たちに、「すぐに出発しなさい」と言った。

あとはこれをポールさんが英訳して下さい。

あっ、なるほど。... の部分しか見てませんでした。

出発 bedeutet 'losfahren' oder 'abreisen', aber nicht 'anfangen'. Dieser Satz ist keine korrekte Übersetzung des Japanischen.

'Er forderte uns auf, sofort abzureisen.' wäre eine mögliche Übersetzung.

Sentence was changed, I suggest deleting the tag.