Generally speaking, it's advisable not to use the Normal Style for anything, as so many other Styles inherit characteristics from it. Rather, you might create your own Styles based on the Normal Style and use those.

Accordingly, you'd create separate paragraph Styles for Hindi and English paragraphs (with whatever font, point size, line spacing, etc. each requires), plus character Styles for Hindi and English that you can use for Hindi text in otherwise-English paragraphs and vice-versa.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]