You can write foreign words, provided that the foreign language uses the same alphabet as the recognition language (the language to which the notebook is set). If it is a word you intend to use regularly you may want to add it to the user dictionary.* Please note that if the word uses accents and special characters not commonly found in the recognition language the dictionary will not be able to apply these to your text. In order to include words that use such accents and special characters, using the keyboard will be necessary. Simply hold your finger on the desired letter for a second longer than you normally would and the keyboard will present you with all of the available alternatives.
*Not available with the Nebo free version on iOS.