Regional accents of English

Non-native speakers of the English language tend to carry the intonation, accent or pronunciation from their mother tongue into the English speech. Even among native speakers, as seen below, many accents exist. Some of the regional accents are easily identified with certain characteristics. Sometimes non-verbal body language also gives away the origin of the speaker.

Another factor is how the English language is taught to young school children. If pronunciation is not taught correctly by the teachers, students will speak in the wrong way too. So there may be systematic mispronunciation coming from a country, such as India, Hong Kong, Malaysia, etc.

Origins in alphabetical order:

Canada:

"A bit about a boat I bought." The diphthong in "about" is a schwa followed by an u. See Canadian raising.

Cantonese (Hong Kong Chinese):

systemetic mispronunciation taught at most schools in Hong Kong due to poor teacher trainning.
trouble with 'r', read as 'l' sound. (opposite of Japanese accent)
trouble with 'v', read as 'w' sound.
trouble with 'wh', read as 'w' sound.
trouble with 'th', read as 'd' sound.
trouble with most ending sounds.
trouble with past tense.
forgetting to add 's' for plurals.
Confusion of 'he', 'she', and sometimes 'it', as all are one "word" in Mandarin Chinese.
tendency to raise their voice unknowingly probably due to high noise pollution in Hong Kong.
trouble with numbers larger than ten thousand, in the Chinese language, ten thousand is read as one myriad, 100 thousand as 10 myriad, one million as 100 myriad etc. Chinese speakers often pause before saying big numbers because of the mental conversion taking place in the head.

East Asia (including Vietnamese, Chinese):

Due to the syllabic nature of their native languages, East Asians tend to drop the ending sound of English words, e.g. "an", "ant", & "and" sound the same.

Finnish:

Due to Finnish always stressing the first syllable, English words accented on the second syllable are often misstressed. "VOcaPUlary".
P and B confused (in Finnish 'p' is pronounced almost the same as 'b').
Difficulty with 'z', pronounced as 's'.

German:

Trouble with 'th', pronounced as 's' or 'z'. (German lacks both [T] and [D].)
's' sometimes also pronounced as 'z'.
'd' , 'g' or 'b' at the end of a word may be pronounced as 't', 'ck' or 'p'.
German doesn't distinguish between adjectives and adverbs, so Germans often drop '-ly' from adverbs.
Use of [ö] for English syllabic [r].

Hebrew:

Hebrew uses a palatalized ("soft") /l'/, whereas English uses a non-palatalized ("hard") /l/
Hebrew has only 5 vowels and generally does not use diphthongs (except for foreign borrowings); Hebrew speakers may therefore mispronounce some of the English vowels.
Hebrew speakers may sometimes gesture or raise their voice in a way which native English speakers may find excessive, although it is considered perfectly normal in Israel.

Italian:

a lot of hand movements.

Japanese:

trouble with 'l', read as 'r' sound. (opposite of Cantonese accent)
tend to over-stress ending sound, e.g. sound as soundo.
often drop articles like "the" and "a"
don't distinguish between singular and plural
trouble with numbers larger than ten thousand, in the Japanese language, ten thousand is read as one myriad, 100 thousand as 10 myriad, one million as 100 myriad etc. Japanese speakers often pause before saying big numbers because of the mental conversion taking place in the head.
often nod their head when they speak as if they are bowing repeatedly.

Mandarin Chinese:

Trouble with final 'm' sound, as 'm' does not occur at the end of a syllable in Mandarin pronunciation, e.g. "time" read as "tine".
Voiced sounds pronounced as their unvoiced counterparts, eg: "duck" for "dog", "root" for "rude". Mandarin does not distinguish /p/ vs. /b/, /t/ vs. /d/, /k/ vs. /g/, etc. (these letters represent aspirated pairs, not voiced pairs, in pinyin)
Confusion of 'he', 'she', and sometimes 'it', as all are one "word" in Mandarin Chinese.
Difficulty with verb tenses in general, as well as plurals. (Mandarin has no direct equivalent to either in its grammar.)
trouble with numbers larger than ten thousand, in the Chinese language, ten thousand is read as one myriad, 100 thousand as 10 myriad, one million as 100 myriad etc. Chinese speakers often pause before saying big numbers because of the mental conversion taking place in the head.

New Zealand English:

American English lax [I] (as in "did") and [U] are centralized in NZ pronunciation, so [dId] --> [did] and [wUd] --> [wud] ("would").
Most other vowels follow British RP style in general form, with minor differences.
NZ English is a non-rhotic dialect.
Has a large vocabulary of words borrowed from the Maori language, and NZ English permits syllable-initial [N] in these borrowings, e.g. (Mount) Ngaruhoe is Maori [Na.ru.ho.e] --> NZE [Næ.ru.hOU] --> USA [ne.ru.hOU]

Farsi (Persian, Iranian):

throat noise in 'k' sound.

Philippines

tend to pronounce /f/ as /p/
often use "he" for females.

Russian:

often a palatalized dental /r'/ is used before vowels, which is absent in English.
lack of differentiation between /x/ (as in "Jose") and /h/ (as in "hot")

The Indian Subcontinent:

Fast speech tempo with choppy syllables
Questions worded like statements. Detected by native speakers because of stress on verb in case of questions.
Using 'ing': Instead of "He has a car", "He is having a car".
English alveolars are perceived by many native Indic and Dravidian language speakers as allophones of retroflex consonants, when Subcontinental dental phonemes are in fact more appropriate equivalents to the English alveolars. This leads to the "hollow" pronunciation of English by many Asian Indians.
they shook their head sideway as they speak as if they are saying no-no-no even when they say yes-yes-yes.

Swedish:

Sing-songy intonation. Swedes often speak English with a melodic intonation, ending sentences on an up-note, much parodized (the Swedish chef from The Muppet Show is a well known example and a Usenet institution.)
Trouble with the ending -ed, as the following sentence (from the parody sitcom Soap): "Do you think I'm finished?" (pronounced "Finnish"). Answer: "No, Swedish!"

USA (Midwest and West Coast):

/O/ merged with /a/. "not" sounds like "naht" (/nOt/ --> [nat]), "opportunity" like "ahppertunity"
preservation of non-prevocalic r
(near Canadian border:) monopthongization of /ow/ as [o], eg. most dialects "boat" /bowt/ --> "boot" [bot]. (To check.)

USA (South):

monopthongization of /ay/ as [a:], eg. most dialects' "I" --> "Ah" in the South.
(also some East Coast:) loss of non-prevocalic r.
slower speech tempo

USA (New England and East Coast):

(also South:) loss of non-prevocalic r in some dialects.
faster speech tempo