... 'English' (and particularly 'Old English') means 'the language of the Angles', who were a bunch of rowdy German immigrants who came over here and took our job er, lives and entire country. (Technically they were one of a few groups of such Germans - the Saxons and the Jutes were also involved; they're also why we're commonly called 'Anglo-Saxon'). So I consider 'English' to be a Germanic tongue, and anything from any other language to be foreign.
The thing is... English comes from England (duh), which is a bit of a mess in terms of invasions. Ignoring the very early stuff, we have:
-The original Britons, who are the principle ancestors of the modern Welsh.
-The Roman invaders, who brought Latin (and later Vulgar Latin ~= Italian) as a language of commerce and government. This is why Welsh, as a language, has a bunch of Latin words - they adopted them back when the Welsh were the British, under Roman rule across the whole island.
-The Angles, Saxons, and assorted other Germans. They (attempted to) completely displace[d] the Britons (and leftover Romans - this was after the Empire collapsed), so 'Old English' - a Germanic language - came in pretty much intact. The Britons got largely driven back to Wales. But, of course, a bunch of words hung around - they always do.
-The Vikings, speaking Old Norse, did a fair amount of invading - at one point they actually ruled all of England except a tiny marshy island, but the Saxon kings came back from that one (somehow). But there's a lot of Viking vocab in English.
-The Normans, in 1066, conquered England, setting themselves up as the ruling elite. They brought Latin (as a formal language) and French with them - which is why the Saxon 'cow' becomes the French 'beef' when it goes to the Lord's table. (As a single example of this, in terms of the nobility: 'King' is Anglo-Saxon; 'Earl' is Norse; 'Count' is French)
--So by this point, the language is more accurately called Anglo-Norman. That's what I tried to demonstrate, but picked a sentence without many French-derived words in it.
And finally:
-The British Empire wreaked merry mayhem with the language. Owning a quarter of the world - plus the current United States, though not at the same time - meant a lot of exposure to new words. That's not just place-specific words (banyan, kangaroo - though we use 'kangaroo court', come to think of it), but a bunch of 'common' words, too: this page gives me words such as 'bungalow', 'loot', and 'shampoo' as Indian (Hindi/Urdu) in origin.
And, as wobbles has pointed out, we've also done our share of adopting words from other languages 'just because'. 'Robot' made its way into English in the same manner that 'sandwich' showed up in French - it comes from the first language to describe it.
(For a really fun time: try and determine the exact moment when each 'invader' suddenly becomes the hero of England's national story. The vile Roman invaders led directly to King Arthur, who fought the filthy Saxon barbarians who later produced the noble King Harald who got shot by the bloodthirsty Normans at Hastings... it's good fun!)
hS