src/transformers/models/marian/convert_marian_to_pytorch.py/add_emb_entries
def add_emb_entries(wemb, final_bias, n_special_tokens=1):
    vsize, d_model = wemb.shape
    embs_to_add = np.zeros((n_special_tokens, d_model))
    new_embs = np.concatenate([wemb, embs_to_add])
    bias_to_add = np.zeros((n_special_tokens, 1))
    new_bias = np.concatenate((final_bias, bias_to_add), axis=1)
    return new_embs, new_bias