From: "bhakti.vikasa.swami" 

Prabhupada: ...any language, you should submit, and you should feel that,

that "I am worthless. My Guru Maharaja has given this chance to serve Krsna,
to offer Krsna... My Lord, I am worthless. I have no capacity to serve You.
But on the order of my Guru Maharaja, I am trying to serve You. Please do
not take any offense. Accept whatever I can do. That's all. That is my
request." That mantra is sufficient. Krsna says in the Bhagavad-gita, yo me
bhaktya prayacchati. Krsna never said that "One who offers Me with Sanskrit
mantra." Yo me bhaktya prayacchati. Real thing is bhakti, feeling: "How to
serve Krsna? How to please Him?" That is wanted. Not to see that you are a
very good scholar in speaking in Sanskrit or English or... That is not...
Always feel that "I am worthless, but I have been, by the grace of my Guru
Maharaja, I have been given the chance. So kindly accept whatever little
service I can give. I am offensive. So kindly excuse me." In this way be
humble, meek, and offer your feeling, and Krsna will be satisfied. Not that
you have to show how you can speak in Sanskrit language.

Ref. VedaBase => Conversation with Devotees -- Hyderabad, April 12, 1975

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The "worthless" mantra