This book *is/was* written *in English by Sam/by Sam in English*.
a. This book was written in English by Sam.
b. This book was written by Sam in English.
Are the two sentences above correct? Are there any differences between them? Which is more common? And I know that Sam did write the book in the "past", so we should use the past tense here, but if we view it as a "fact", can I say "is" instead of "was"? Thanks!

Question

Answer

They are both correct. Sentence A is much more common. Sentence B sounds like the speaker added "in English" to the end of the sentence (and thus had not planned to mention it in the first place). This effect makes the sentence sound awkward.

You must use "was written". You could use "is written" if the work was a continuous production, such as a newspaper or blog. Example: "This blog is written by John."