Some encyclopedias, published in English-speaking countries, have been created with the help of international contributors with hands-on expertise. Moreover, the encyclopedias have been compiled and printed through the professional use of modern equipment. That is why, their readers should expect a high-end product, indeed. But, in certain respect it is not true. The sources they list at the end of entries are primarily in English. Such superficial approach doesn't provide us with thorough knowledge.