In this tutorial Machine translation with transformer 2, the colab cell break because spaCy dependency break, that leads to can’t load tokenizer error.
The original installation is this
# pip install -U spacy
# python -m spacy download en_core_web_sm
# python -m spacy download de_core_news_sm

The fix is this (validated by me)
pip install spacy==2.2.1
python -m spacy download en
python -m spacy download de