see #12: use en-us as default language of readme

book/en-us/00-preface.md

@@ -11,11 +11,11 @@ order: 0
 ## Introduction
 
 C++ user group is a fairly large. From the advent of C++98 to the official finalization of C++11, it has accumulated over a decade. C++14/17 is an important complement and optimization for C++11, and C++20 brings this language to the door of modernization. The extended features of all these new standards are given to the C++ language. Infused with new vitality.
-C++ programmers, who are still using traditional C++** (this book refers to C++98 and its previous C++ standards as traditional C++), may even amzed by the fact that they are not using the same language while reading C++11/14/17/20 code.
+C++ programmers, who are still using **traditional C++** (this book refers to C++98 and its previous C++ standards as traditional C++), may even amzed by the fact that they are not using the same language while reading C++11/14/17/20 code.
 
 **Modern C++** (this book refers to C++11/14/17/20) introduces a lot of features into traditional C++, which makes the whole C++ become language that modernized. Modern C++ not only enhances the usability of the C++ language itself, but the modification of the `auto` keyword semantics gives us more confidence in manipulating extremely complex template types. At the same time, a lot of enhancements have been made to the language runtime. The emergence of Lambda expressions has made C++ have the "closure" feature of "anonymous functions", which is almost in modern programming languages ​​(such as Python/Swift/.. It has become commonplace, and the emergence of rvalue references has solved the problem of temporary object efficiency that C++ has long been criticized.
 
-C++17 is the direction that has been promoted by the C++ community in the past three years. It also points out an important development direction of modern C++** programming. Although it does not appear as much as C++11, it contains a large number of small and beautiful languages ​​and features (such as structured binding), and the appearance of these features once again corrects our programming paradigm in C++.
+C++17 is the direction that has been promoted by the C++ community in the past three years. It also points out an important development direction of **modern C++** programming. Although it does not appear as much as C++11, it contains a large number of small and beautiful languages ​​and features (such as structured binding), and the appearance of these features once again corrects our programming paradigm in C++.
 
 Modern C++ also adds a lot of tools and methods to its own standard library, such as `std::thread` at the level of the language itself, which supports concurrent programming and no longer depends on the underlying system on different platforms. The API implements cross-platform support at the language level; `std::regex` provides full regular expression support and more. C++98 has been proven to be a very successful "paradigm", and the emergence of modern C++ further promotes this paradigm, making C++ a better language for system programming and library development. Concepts provide verification on the compile-time of template parameters, further enhancing the usability of the language.
 

book/en-us/01-intro.md

@@ -36,9 +36,9 @@ Before learning modern C++, let's take a look at the main features that have bee
 
 - **`register` keyword is deprecated and can be used but no longer has any practical meaning.**
 
-- The `++` operation of the **`bool` type is deprecated.**
+- **The `++` operation of the `bool` type is deprecated.**
 
-- ** If a class has a destructor, the properties for which it generates copy constructors and copy assignment operators are deprecated.**
+- **If a class has a destructor, the properties for which it generates copy constructors and copy assignment operators are deprecated.**
 
 - **C language style type conversion is deprecated (ie using `(convert_type)`) before variables, and `static_cast`, `reinterpret_cast`, `const_cast` should be used for type conversion.**