Yes, it is important to take length into account. Text or translation extension can make your design vary considerably. For example, words in German tend to be longer than in English.
And not only that, the grammatical structure of each language also varies, so it is advisable to establish sentences as text strings instead of as single words since the order might not be correct in the translation. In this sense, we must also take into account aspects such as gender, singular and plural, and even syllabic separation.
For example, if we compare the English and Spanish translations of this sentence: 'Se han añadido {numero} items a tu carrito' vs. '{numero} items have been added to your cart', we can see that the sentence structure completely changes depending on the language and this must be taken into account in the development.
Finally, it is worth mentioning the direction of script. A page in Arabic that is read right to left will not have the same layout as one in Romanian, which is left to right. So reading direction is an important aspect to take into account in the design phase.