"Is this construction valid in any (or all?) varieties of English?" – Yes, the "construction" is; the semantics may not be, though.

There's nothing "unAmerican" about it either.

"My … ear hears that last one as...troublesome." – all ears ought to find it so, it's semantically awkward/ maybe even invalid (fails to make sense to some?), yet it works.

[All English][1]: twice larger than had a respectable life, dominated over two times larger than for some time around (late) 1800s, and continues to lead a quiet and comfortable life today.

See also: [AmE][2]; [BrE][3]

This answer is not based on interpretation of nGrams – I started off with the answer, and then found nGrams to be supportive, to some extent, of what I wanted to say.
[1]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0 [2]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=17&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0 [3]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=18&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0

"Is this construction valid in any (or all?) varieties of English?" – Yes, the "construction" is; the semantics may not be, though.

There's nothing "unAmerican" about it either.

"My … ear hears that last one as...troublesome." – all ears ought to find it so, it's semantically awkward/ maybe even invalid (fails to make sense to some?), yet it works.

All English: twice larger than had a respectable life, dominated over two times larger than for some time around (late) 1800s, and continues to lead a quiet and comfortable life today.

See also: AmE; BrE

This answer is not based on interpretation of nGrams – I started off with the answer, and then found nGrams to be supportive, to some extent, of what I wanted to say.

"Is this construction valid in any (or all?) varieties of English?" – Yes, the "construction" is; the semantics may not be, though.

There's nothing "unAmerican" about it either.

"My … ear hears that last one as...troublesome." – all ears ought to find it so, it's semantically awkward/ maybe even invalid (fails to make sense to some?), yet it works.

[All English][1]: twice larger than had a respectable life, dominated over two times larger than for some time around (late) 1800s, and continues lead a quiet and comfortable life today.

See also: [AmE][2]; [BrE][3]

This answer is not based on interpretation of nGrams – I started off with the answer, and then found nGrams to be supportive, to some extent, of what I wanted to say.
[1]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0 [2]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=17&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0 [3]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=18&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0

"Is this construction valid in any (or all?) varieties of English?" – Yes, the "construction" is; the semantics may not be, though.

There's nothing "unAmerican" about it either.

"My … ear hears that last one as...troublesome." – all ears ought to find it so, it's semantically awkward/ maybe even invalid (fails to make sense to some?), yet it works.

[All English][1]: twice larger than had a respectable life, dominated over two times larger than for some time around (late) 1800s, and continues to lead a quiet and comfortable life today.

See also: [AmE][2]; [BrE][3]

This answer is not based on interpretation of nGrams – I started off with the answer, and then found nGrams to be supportive, to some extent, of what I wanted to say.
[1]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0 [2]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=17&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0 [3]: https://books.google.com/ngrams/graph?content=two%20times%20larger%20than%2Ctwice%20larger%20than&year_start=1800&year_end=2000&corpus=18&smoothing=3&share=&direct_url=t1%3B%2Ctwo%20times%20larger%20than%3B%2Cc0%3B.t1%3B%2Ctwice%20larger%20than%3B%2Cc0