Change command-tab to option-tab on Mac

Use KeyRemap4MacBook:

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⌥⇥ is already used for inserting tabs in text fields, entering outline mode in TextEdit, and focusing elements in Safari.

Adding this to private.xml would change ⌘⇥ to ⌃⇥ and ⇧⌘⇥ to ⌃⇧⇥:

<autogen>__KeyToKey__ KeyCode::TAB, VK_COMMAND | ModifierFlag::NONE, KeyCode::TAB, ModifierFlag::CONTROL_L</autogen>
<autogen>__KeyToKey__ KeyCode::TAB, VK_SHIFT | VK_COMMAND | ModifierFlag::NONE, KeyCode::TAB, ModifierFlag::CONTROL_L, ModifierFlag::SHIFT_L</autogen>

You can change the shortcuts of menu bar items from System Preferences:

When I first got a Mac, I tried to do this, too. It doesn't work, because there isn't a one-to-one correspondence; that is, the Option key doesn't always correspond to the Alt key.

When I was in college, we still used mechanical typewriters. I had two typewriters, one for each language I used. After a while, I had no difficulty switching between the two even though the layout was different.

The best thing to do is just get used to the Mac. You'll develop bilingual muscle memory.