There isn't such a built-in feature within Types plugin, you might consider custom codes, for example:
1) Setup a custom select field, field title is "Countries", see screenshot Countries.JPG
2) Use wpt_field_options filter hook to change options of above select field to what you want, like this:
add_filter('wpt_field_options', function($options, $title, $type){
if($title == 'Countries'){
$country = [
'hot'=>[
["中国大陆","86"],
["香港","852"],
["澳门","853"],
["台湾","886"],
["美国","1"],
["日本","81"],
],
"a"=>[
["阿尔巴尼亚","355"],
["阿尔及利亚","213"],
["阿富汗","93"],
["阿根廷","54"],
["阿鲁巴岛","297"],
["阿曼","968"],
["阿塞拜疆","994"],
["阿森松(英)","247"],
["埃及","20"],
["埃塞俄比亚","251"],
["爱尔兰","353"],
["爱沙尼亚","372"],
["安道尔","376"],
["安哥拉","244"],
["安圭拉岛(英)","1264"],
["安提瓜和巴布达","1268"],
["奥地利","43"],
["澳大利亚","61"],
["澳门","853"],
],
'b'=>[
["巴巴多斯","1246"],
["巴布亚新几内亚","675"],
["巴哈马国","1242"],
["巴基斯坦","92"],
["巴拉圭","595"],
["巴林","973"],
["巴拿马","507"],
["巴西","55"],
["白俄罗斯","375"],
["百慕大群岛(英)","1441"],
["保加利亚","359"],
["贝宁","229"],
["比利时","32"],
["冰岛","354"],
["波多黎各(美)","1"],
["波兰","48"],
["波斯尼亚和黑塞哥维那","387"],
["玻利维亚","591"],
["伯利兹","501"],
["博茨瓦纳","267"],
["不丹","975"],
["布基纳法索","226"],
["布隆迪","257"],
],
'c'=>[
["朝鲜","850"],
["赤道几内亚","240"],
],
'd'=>[
["丹麦","45"],
["德国","49"],
["东萨摩亚(美)","1684"],
["多哥","228"],
["多米尼加共和国","1809"],
["多米尼克国","1767"],
],
'e'=>[
["俄罗斯","7"],
["厄瓜多尔","593"],
["厄立特里亚","291"],
],
'f'=>[
["法国","33"],
["法罗群岛(丹)","298"],
["法属波里尼西亚","689"],
["梵蒂冈","14397"],
["菲律宾","63"],
["斐济","679"],
["芬兰","358"],
["佛得角","238"],
["福克兰群岛","500"],
],
'g'=>[
["冈比亚","220"],
["刚果","242"],
["哥伦比亚","57"],
["哥斯达黎加","506"],
["格林纳达","1473"],
["格陵兰岛","299"],
["格鲁吉亚","995"],
["古巴","53"],
["瓜德罗普岛(法)","590"],
["关岛(美)","1671"],
["圭亚那","592"],
],
'h'=>[
["哈萨克斯坦","7"],
["海地","509"],
["韩国","82"],
["荷兰","31"],
["荷属安的列斯群岛","599"],
["洪都拉斯","504"],
["基里巴斯","686"],
],
'j'=>[
["吉布提","253"],
["吉尔吉斯斯坦","996"],
["几内亚","224"],
["几内亚比绍","245"],
["加拿大","1"],
["加纳","233"],
["加蓬","241"],
["柬埔塞","855"],
["捷克","420"],
["津巴布韦","263"],
],
'k'=>[
["喀麦隆","237"],
["卡塔尔","974"],
["开曼群岛(英)","1345"],
["科科斯岛","61"],
["科克群岛(新)","682"],
["科摩罗","269"],
["科特迪瓦","225"],
["科威特","965"],
["克罗地亚","385"],
["肯尼亚","254"],
],
'l'=>[
["拉脱维亚","371"],
["莱索托","266"],
["老挝","856"],
["黎巴嫩","961"],
["立陶宛","370"],
["利比里亚","231"],
["利比亚","218"],
["列支敦士登","423"],
["留尼汪岛","262"],
["卢森堡","352"],
["卢旺达","250"],
["罗马尼亚","40"],
],
'm'=>[
["马达加斯加","261"],
["马尔代夫","960"],
["马耳他","356"],
["马拉维","265"],
["马来西亚","60"],
["马里","223"],
["马里亚纳群岛","1670"],
["马其顿","389"],
["马绍尔群岛","692"],
["马提尼克(法)","596"],
["马约特岛","262"],
["毛里求斯","230"],
["毛里塔尼亚","222"],
["美国","1"],
["蒙古","976"],
["蒙特塞拉特岛(英)","1664"],
["孟加拉国","880"],
["秘鲁","51"],
["密克罗尼西亚(美)","691"],
["缅甸","95"],
["摩尔多瓦","373"],
["摩洛哥","212"],
["摩纳哥","377"],
["莫桑比克","258"],
["墨西哥","52"],
],
'n'=>[
["纳米比亚","264"],
["南非","27"],
["南斯拉夫","381"],
["瑙鲁","674"],
["尼泊尔","977"],
["尼加拉瓜","505"],
["尼日尔","227"],
["尼日利亚","234"],
["纽埃岛(新)","683"],
["挪威","47"],
["诺福克岛(澳)","672"],
],
'p'=>[
["帕劳(美)","680"],
["葡萄牙","351"],
],
'r'=>[
["日本","81"],
["瑞典","46"],
["瑞士","41"],
],
's'=>[
["萨尔瓦多","503"],
["塞拉利昂","232"],
["塞内加尔","221"],
["塞浦路斯","357"],
["塞舌尔","248"],
["桑给巴尔","259"],
["沙特阿拉伯","966"],
["圣诞岛","61"],
["圣多美和普林西比","239"],
["圣赫勒拿","290"],
["圣克里斯托弗和尼维斯","1869"],
["圣卢西亚","1758"],
["圣马力诺","378"],
["圣皮埃尔岛及密克隆岛","508"],
["圣文森特岛(英)","1784"],
["斯里兰卡","94"],
["斯洛伐克","421"],
["斯洛文尼亚","386"],
["斯威士兰","268"],
["苏丹","249"],
["苏里南","597"],
["所罗门群岛","677"],
["索马里","252"],
],
't'=>[
["塔吉克斯坦","992"],
["台湾","886"],
["泰国","66"],
["坦桑尼亚","255"],
["汤加","676"],
["特克斯和凯科斯群岛(英)","1649"],
["特立尼达和多巴哥","1868"],
["突尼斯","216"],
["图瓦卢","688"],
["土耳其","90"],
["土库曼斯坦","993"],
],
'w'=>[
["瓦努阿图","678"],
["危地马拉","502"],
["维尔京群岛(英)","1340"],
["委内瑞拉","58"],
["乌干达","256"],
["乌克兰","380"],
["乌拉圭","598"],
["乌兹别克斯坦","998"],
],
'x'=>[
["西班牙","34"],
["西萨摩亚","685"],
["希腊","30"],
["香港","852"],
["新加坡","65"],
["新喀里多尼亚群岛(法)","687"],
["新西兰","64"],
["匈牙利","36"],
["叙利亚","963"],
],
'y'=>[
["牙买加","1876"],
["亚美尼亚","374"],
["也门","967"],
["伊拉克","964"],
["伊郎","98"],
["以色列","972"],
["意大利","39"],
["印度","91"],
["印度尼西亚","62"],
["英国","44"],
["约旦","962"],
["越南","84"],
],
'z'=>[
["赞比亚","260"],
["乍得","235"],
["直布罗陀(英)","350"],
["智利","56"],
["中非","236"],
["中国大陆","86"],
]
];
foreach($country as $k1 => $arr){
if(is_array($arr)){
foreach($arr as $k2=> $v){
$options[] = array(
'#value' => $v[1],
'#title' => $v[0]
);
}
}
}
}
return $options;
}, 10, 3);