You're right in that a Japanese character usually holds more sound than an individual letter from the Roman alphabet does, so the secret messages are fuller phrases in the original compared to these translations (not that I blame the translator, this would've been tough to do). The messages in the original Japanese, for reference:
- た・ん・と・う・か・え・て = ta-n-to-u-ka-e-te = "tantou kaete" aka "replace/switch editor"
- た・ぬ・き・が・い・っ・ぱ・い = ta-nu-ki-ga-i-p-pa-i = "tanuki ga ippai" aka "full of tanuki/so many tanuki"