According to Black’s law dictionary “shall“ means “is required to“ or “has a duty to”. The German „sollen“, on the other hand, describes a general rule, which may be deviated from in exceptional circumstances (cf. Handbuch der Rechtsförmlichkeit).
Clearly translating a duty with a strong suggestion is wrong and can have a negative impact. For example:
“The purchaser shall pay the purchase price on the first day of the month following the receipt of the goods.” expresses a clear legal duty. Breaching that duty, e.g. paying on the fifth day, may lead to liability for damages.
However, if one were to translate that as “Der Käufer soll den Kaufpreis am ersten Tag des Monats zahlen, der auf den Erhalt der Ware folgt.”, this would not constitute such a clear legal obligation (this would be more of a wish or a suggestion), so that payment on the fifth day would not constitute a payment default and therefore would not give rise to a claim for damages.
In German legal language, legal duties are usually expressed in the indicative mood of the verb. Further possible translations for “shall” are “haben zu” and “verpflichtet sein”.